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Upgrading & Repairing PCs Eighth Edition

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# Input Devices

- Keyboards
  - Types of Keyboards
  - Keyboard Technology
  - Keyboard Troubleshooting and Repair
  - Reference Material
- Mice
  - Microsoft IntelliMouse
  - Mouse Interface Types
  - Mouse Troubleshooting
  - Trackpoint II/III
  - Glidepoint
- Game Adapter (Joystick) Interface

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This chapter discusses input devices--the devices used to communicate with the computer. The most common input device is, of course, the keyboard, and this chapter discusses keyboards in depth. It also discusses mice and other pointing device alternatives because they are now a standard requirement for operating a modern PC with a GUI (graphical user interface) such as Windows or OS/2. Finally, this chapter also discusses the game or joystick interface, which is used to input signals from a joystick, paddles, or other game devices.

## Keyboards

One of the most basic system components is your keyboard. The keyboard is the primary input device. It is used for entering commands and data into the system. This section looks at the keyboards available for PC-compatible systems. It examines the different types of keyboards, how the keyboard functions, the keyboard-to-system interface, and keyboard troubleshooting and repair.

### Types of Keyboards

Over the years since the introduction of the original IBM PC, IBM has created three different keyboard designs for PC systems, and Microsoft has augmented one of them. They have become standards in the industry and are shared by virtually all of the PC-compatible manufacturers. More recently with the introduction of Windows 95, a modified version of the 101-key design (created by Microsoft) has appeared. The primary keyboard types are:

- 83-key PC and XT keyboard
- 84-key AT keyboard
- 101-key enhanced keyboard
- 104-key enhanced Windows keyboard

This section discusses each keyboard type, and shows their layout and physical appearance. Because most systems use keyboards based on the 101- and 104-key enhanced keyboard designs, these versions are emphasized.

83-Key PC and XT Keyboard

When the original PC was first introduced, it had something that few other personal computers had at the time: an external detachable keyboard. Most other small personal computers of the time had the keyboard built in, like the Apple II. Although the external design was a good move on IBM's part, the keyboard design was not without its drawbacks. One of the most criticized components of the original 83-key keyboard is the awkward layout (see Figure 9.1). The Shift keys are small and in the wrong place on the left side. The Enter key is also too small. These oversights were especially irritating at the time because IBM had produced the Selectric typewriter, perceived as a standard for good keyboard layout.

FIG. 9.1 PC and XT 83-key keyboard layout.

This keyboard has a built-in processor that communicates with the motherboard via a special serial data link. The communication is one-way, which means that the mother-board cannot send commands or data back to the keyboard. For this reason, IBM 83-key keyboards have no Light Emmiting Diode (LED) indicator lights. Because the status of the Caps Lock, Num Lock, and Scroll Lock are maintained by the motherboard, there is no way to make sure that any LED indicator lights remain in sync with the actual status of the function.

Many aftermarket (non-IBM) PC keyboards added the lights, and the keyboard attempted to keep track of the three functions independently of the motherboard. This worked in most situations, but it was entirely possible to see the LEDs become out of sync with the actual function status. Rebooting corrected this temporary problem, but it was annoying nonetheless.

The original 83-key PC/XT keyboard is no longer used and is not electrically compatible with AT-compatible motherboards, although some aftermarket units may be compatible by moving an XT/AT switch usually found on the bottom of the keyboard.

84-Key AT Keyboard

When the AT was introduced in 1984, it included a new keyboard--the 84-key unit (see Figure 9.2). This keyboard corrected many problems of the original PC and XT keyboards. The position and arrangement of the numeric keypad was modified. The Enter key was made much larger, like that of a Selectric typewriter. The Shift key positions and sizes were corrected. IBM also finally added LED indicators for the status of the Caps Lock, Scroll Lock, and Num Lock toggles.

FIG. 9.2 AT 84-key keyboard layout.

These keyboards use a slightly modified interface protocol that is bi-directional. This means that the processor built into the keyboard can talk to another processor (called the 8042 keyboard controller chip) built into the motherboard. The keyboard controller on the motherboard can send commands and data to the keyboard, which allows functions such as changing the keyboard typematic (or repeat) rate as well as the delay before repeating begins. The keyboard controller on the motherboard also performs scan code translation, which allow a much easier integration of foreign language keyboards into the system. Scan codes are the names for the hexadecimal codes actually sent by the keyboard to the motherboard. The bi-directional interface can be used to control the LED indicators on the keyboard, thus ensuring that the status of a particular function and the corresponding indicator are always in sync.

The 84-key unit that came with the original AT system is no longer used, although its electrical design is compatible with newer systems. It lacks some of the keys found in the newer keyboards and does not have as nice a numeric keypad section, but many users prefer the more Selectric-style layout of the alphanumeric keys. Likewise, some users prefer to have the 10 function keys arranged on the left-hand side as opposed to the enhanced arrangement in which 12 function keys are lined up along the top.

Enhanced 101-Key (or 102-Key) Keyboard

In 1986, IBM introduced the "corporate" enhanced 101-key keyboard for the newer XT and AT models (see Figure 9.3). I use the word "corporate" because this unit first appeared in IBM's RT PC, which is a RISC (Reduced Instruction Set Computer) system designed for scientific and engineering applications; keyboards with this design are now supplied with virtually every type of system and terminal that IBM sells. Other companies quickly copied this design, and it has been the standard in PC-compatible systems ever since.

This universal keyboard has a further improved layout over that of the 84-key unit, with perhaps the exception of the Enter key, which reverted to a smaller size. The 101-key enhanced keyboard was designed to conform to international regulations and specifications for keyboards. In fact, other companies such as Digital Equipment Corporation (DEC) and Texas Instruments (TI) had already been using designs similar to the IBM 101-key unit. The IBM 101-key units originally came in versions with and without the status indicator LEDs, depending on whether the unit was sold with an XT or AT system. Now there are many other variations to choose from, including some with integrated pointing devices.

FIG. 9.3 101-key enhanced keyboard layout.

The enhanced keyboard is available in several different variations, but all are basically the same electrically and can be interchanged. IBM and its Lexmark keyboard and printer subsidiary have produced a number of versions, including keyboards with built-in pointing devices and new ergonomic layouts. Most of the enhanced keyboards attach to the system via the standard 5-pin DIN (Deutsche Industrie Norm) connector, but many others come with cables for the 6-pin mini-DIN connector found on many newer systems, including the IBM PS/2s and most Slimline compatibles. Although the connectors may be physically different, the keyboards are not, and you can either interchange the cables or use a cable adapter to plug one type into the other.

The 101-key keyboard layout can be divided into the following four sections:

- Typing area
- Numeric keypad
- Cursor and screen controls
- Function keys

The 101-key arrangement is similar to the Selectric keyboard layout with the exception of the Enter key. The Tab, Caps Lock, Shift, and Backspace keys have a larger striking area and are located in the familiar Selectric locations. Ctrl and Alt keys are on each side of the space bar. The typing area and numeric keypad have home-row identifiers for touch typing.

The cursor and screen-control keys have been separated from the numeric keypad, which is reserved for numeric input. (As with other PC keyboards, you can use the numeric keypad for cursor and screen control when the keyboard is not in Num Lock mode.) A division-sign key and an additional Enter key have been added to the numeric keypad.

The cursor-control keys are arranged in the inverted T format. The Insert, Delete, Home, End, Page Up, and Page Down keys, located above the dedicated cursor-control keys, are separate from the numeric keypad. The function keys, spaced in groups of four, are located across the top of the keyboard. The keyboard has two additional function keys: F11 and F12. The Esc key is isolated in the upper-left corner of the keyboard. Dedicated Print Screen/Sys Req, Scroll Lock, and Pause/Break keys are provided for commonly used functions.

Foreign language versions of the enhanced keyboard include 102-keys and a slightly different layout from the 101-key U.S. versions.

One of the many useful features of the enhanced keyboard is removable keycaps. With clear keycaps and paper inserts, you can customize the keyboard. Keyboard templates are also available to provide specific operator instructions.

The enhanced keyboard will probably come with any PC-compatible desktop system for quite some time. It is currently the most popular design and does not show any signs of being replaced in the future. Because most compatible systems use this same type of keyboard, it is relatively easy to move from one system to another without relearning the layout.

104-Key Windows Keyboard

If you are a touch typist like I am, then you really hate to take your hands off of the keyboard to use a mouse. Windows 95 makes this even more of a problem, because it exploits both mouse buttons. Many new keyboards, especially those in portable computers, include a variation of the IBM Trackpoint or the Alps Glidepoint (both of which are discussed later in this chapter), which allow touch typists to keep their hands on the keyboard even while moving the pointer, but there is still another alternative that can help. Microsoft has come up with a specification that calls for three new Windows-specific keys to be added to the keyboard. These new keys help with functions that would otherwise require multiple keystrokes or mouse clicks.

Microsoft has released a Windows keyboard specification that outlines a set of new keys and key combinations. The familiar 101-key layout grows to 104 keys, with the addition of left and right Windows keys and an Application key. These keys will be used for operating-system and application-level keyboard combinations, similar to today's Ctrl and Alt combinations. You don't need the new keys to use Windows 95 or NT, but software vendors are starting to add specific functions to their Windows products that will use the new Application key (which is the same as the right mouse button). Figure 9.4 shows the standard Windows keyboard layout including the three new keys.

FIG. 9.4 104-key Windows keyboard layout.

The recommended Windows keyboard layout calls for the Left and Right Windows keys (called WIN keys) to flank the Alt keys on each side of the space bar, and an Application key on the right of the Right Windows key. Note that the exact placement of these keys is up to the keyboard designer, so you will see variations from keyboard to keyboard.

The WIN keys open the Start menu, which then can be navigated with the arrow keys. The Application key simulates the right mouse button; in most applications, it brings up context-sensitive pop-up menus. Several WIN key combinations offer preset macro commands as well. For example, you press WIN+E to bring up the Windows Explorer. The following table shows a list of all the new Windows 95 key combinations:

Key Combination | Action
WIN+R | Displays the Run dialog box.
WIN+M | Minimizes All.
Shift+WIN+M | Undoes Minimize All.
WIN+F1 | Starts Help.
WIN+E | Starts Windows Explorer.
WIN+F | Finds files or folders.
Ctrl+WIN+F | Finds the computer.
WIN+Tab | Cycles through taskbar buttons.
WIN+Break | Displays the System properties dialog box.

The Windows keyboard specification requires that keyboard makers increase the number of trilograms in their keyboard designs. A trilogram is a combination of three rapidly pressed keys that perform a special function, such as Ctrl+Alt+Delete. Designing a keyboard so that the switch matrix will correctly register trilograms is expensive, and this plus the additional Windows keys themselves will cause the price of these keyboards to rise. Volume sales should keep the price reasonable, as well as the natural market competition.

Virtually every keyboard manufacturer is now producing keyboards with these Windows-specific keys. Some are also combining these new keys with other features. For example, besides the new Windows keys, the Microsoft Natural Keyboard includes ergonomic features, such as split keypads that are rotated out from the middle to encourage a straight wrist position. It takes some getting used to. Unfortunately, this keyboard (made by Keytronics for Microsoft) does not have nearly the feel of the mechanical switch designs like Alps, Lite-On, or NMB, or the extremely high-quality feel of the Lexmark keyboards.

In addition to the Windows keys, other companies like Lexmark, NMB, and Alps have licensed a new space bar design called Erase-Ease from Keyboard Enhancements, Inc. This new design splits the space bar into two parts, using the shorter left (or optionally the right) half as an additional Backspace key. If you see a keyboard advertising 105-keys, then it probably has both the three additional Windows keys plus the extra Backspace key next to the space bar.

Although the new Windows keys are not mandatory when running Windows, and certainly not everybody will have them, I do expect more and more new PC systems to include keyboards with these extra keys. They can make it easier for both experienced touch typists as well as novice users to access some of the functions of Windows and their applications.

Compatibility

The 83-key PC/XT type is different from all the others and normally plugs into only 8-bit PC/XT systems that do not use the motherboard-based 8042-type keyboard controller chip. This is definitely true for IBM's keyboards and also is true for many compatible units. Some compatibles may be switchable to work with an AT-type motherboard via an XT/AT switch.

The 84-key unit from IBM works on only AT-type 16-bit (or greater) motherboards and does not work at all with PC/XT systems. Again, some aftermarket designs may have an XT/AT switch to allow for compatibility with PC/XT-type systems. If you have the keyboard set in the wrong mode, it will not work, but no damage will occur.

The enhanced keyboards from IBM are universal and auto-switching, which means that they work in virtually any system from the XT to the PS/2 or any PC-compatible by simply plugging them in. Some may require that a switch be moved on the keyboard to make it compatible with PC/XT systems that do not have the 8042-type keyboard controller on the motherboard. In some cases, you may also need to switch to a different cable with the proper system end connector, or use an adapter.

Although the enhanced keyboard is electrically compatible with any AT-type mother-board and even most PC/XT-type motherboards, many older systems will have software problems using these keyboards. IBM changed the ROM on the systems to support the new keyboard properly, and the compatible vendors followed suit. Very old (1986 or earlier) machines may require a ROM upgrade to use properly some of the features on the 101-key enhanced keyboards, such as the F11 and F12 keys. If the individual system ROM BIOS is not capable of operating the 101-key keyboard correctly, the 101-key keyboard may not work at all (as with all three ROM versions of the IBM PC); the additional keys (F11 and F12 function keys) may not work; or you may have problems with keyboard operation in general. In some cases, these compatibility problems cause improper characters to appear when keys are typed (causing the system to beep), and general keyboard operation is a problem. These problems can often be solved by a ROM upgrade to a newer version with proper support for the enhanced keyboard.

If you have an older IBM system, you can tell whether your system has complete ROM BIOS support for the 101-key unit: When you plug in the keyboard and turn on the system unit, the Num Lock light automatically comes on and the numeric keypad portion of the keyboard is enabled. This method of detection is not 100 percent accurate, but if the light goes on, your BIOS generally supports the keyboard. A notable exception is the IBM AT BIOS dated 06/10/85; it turns on the Num Lock light, but still does not properly support the enhanced keyboard. All IBM BIOS versions dated since 11/15/85 have proper support for the enhanced keyboards.

In IBM systems that support the enhanced keyboard, if it is detected on power up, Num Lock is enabled and the light goes on. If one of the older 84-key AT-type keyboards is detected, the Num Lock function is not enabled because these keyboards do not have arrow keys separate from the numeric keypad. When the enhanced keyboards first appeared in 1986, many users (including me) were irritated on finding that the numeric keypad was automatically enabled every time the system boots. Most compatibles began integrating a function into the system setup that allowed specification of the Num Lock status on boot.

Some thought that the automatic enabling of Num Lock was a function of the enhanced keyboard because none of the earlier keyboards seemed to operate this way. Remember that this function is not really a keyboard function; it is a function of the motherboard ROM BIOS, which identifies an enhanced 101-key unit and turns on the Num Lock as a "favor." In systems that cannot disable the automatic numeric keypad enable feature, you can use the DOS 6.0 or higher version `NUMLOCK=` parameter in CONFIG.SYS to turn Num Lock on or off as desired. If you are running a version of DOS earlier than 6.0, you can use one of the many public domain programs available for turning off the Num Lock function. Inserting the program to disable Num Lock in the AUTOEXEC.BAT file turns off the numeric keypad whenever the system reboots.

In an informal test, I plugged the new keyboard into an earlier XT. The keyboard seemed to work well. None of the keys that did not exist previously, such as F11 and F12, were operable, but the new arrow keys and the numeric keypad worked. The enhanced keyboard seems to work on XT or AT systems, but it does not function on the original PC systems because of BIOS and electrical interface problems. Many compatible versions of the 101-key enhanced keyboards have a manual XT/AT switch on the bottom that may allow the keyboard to work in an original PC system.

### Keyboard Technology

The technology that makes up a typical PC keyboard is very interesting. This section focuses on all aspects of keyboard technology and design, including the key switches, the interface between the keyboard and the system, scan codes, and the keyboard connectors.

Key Switch Design

Several types of switches are used in keyboards today. Most keyboards use one of several variations on a mechanical key switch. A mechanical key switch relies on a mechanical momentary contact type switch to make electrical contact in a circuit. Some high-end keyboard designs use a totally different nonmechanical design that relies on capacitive switches. This section discusses these switches and the highlights of each design. The most common type of key switch is the mechanical type, available in the following variations:

- Pure mechanical
- Foam element
- Rubber dome
- Membrane

The pure mechanical type is just that--a simple mechanical switch that features metal contacts in a momentary contact arrangement. Often a tactile feedback mechanism-- consisting of a clip and spring arrangement to give a "clicky" feel to the keyboard and offer some resistance to pressing the key--is built in. Several companies, including Alps Electric, Lite-On, and NMB Technologies, manufacture this type of keyboard using switches primarily from Alps Electric. Mechanical switches are very durable, usually have self-cleaning contacts, and normally are rated for 20 million keystrokes, which is second only to the capacitive switch. They also offer excellent tactile feedback.

Foam element mechanical switches were a very popular design in some older keyboards. Most of the older compatible keyboards, including those made by Keytronics and many others, use this technology. These switches are characterized by a foam element with an electrical contact on the bottom that is mounted on the bottom of a plunger attached to the key itself (see Figure 9.5).

FIG. 9.5 Typical foam element mechanical key switch.

When the switch is pressed, a foil conductor on the bottom of the foam element closes a circuit on the printed circuit board below. A return spring pushes the key back up when the pressure is released. The foam dampens the contact, helping to prevent bounce, but unfortunately gives these keyboards a "mushy" feel. The big problem with this type of key switch design is that there is often little in the way of tactile feedback, and systems with these keyboards often resort to tricks such as clicking the PC's speaker to signify that contact has been made. Compaq has used keyboards of this type (made by Key-tronics) in many of their systems, but perhaps the most popular user today is Packard Bell. Preferences in keyboard feel are somewhat subjective; I personally do not favor the foam element switch design.

Another problem with this type of design is that it is prone to corrosion on the foil conductor and the circuit board traces below. When this happens, the key strikes may become intermittent, which can be frustrating. Fortunately, these keyboards are among the easiest to clean. By disassembling this type of keyboard completely, you can usually remove the circuit board portion without removing each foam pad separately, and expose the bottoms of all the pads. Then you can easily wipe the corrosion and dirt off the bottom of the foam pads and the circuit board, thus restoring the keyboard to a "like-new" condition. Unfortunately, over time the corrosion problem will occur again. I recommend using some Stabilant 22a from D.W. Electrochemicals to improve the switch contact action and to prevent future corrosion. Because of problems like this, the foam element design is not used much anymore and has been superseded in popularity by the rubber dome design.

Rubber dome switches are mechanical switches that are similar to the foam element-type but are improved in many ways. Instead of a spring, these switches use a rubber dome that has a carbon button contact on the underside. As you press a key, the key plunger presses on the rubber dome, causing it to resist and then collapse all at once, much like the top of an oil can. As the rubber dome collapses, the user feels the tactile feedback, and the carbon button makes contact between the circuit board traces below. When the key is released, the rubber dome re-forms and pushes the key back up.

The rubber eliminates the need for a spring and provides a reasonable amount of tactile feedback without any special clips or other parts. A carbon button is used because it is resistant to corrosion and also has a self-cleaning action on the metal contacts below. The rubber domes are formed into a sheet that completely protects the contacts below from dirt, dust, and even minor spills. This type of design is the simplest, using the fewest parts. These things make this type of keyswitch very reliable and help make rubber dome-type keyboards the most popular in service today.

If rubber dome keyboards have a drawback at all, it is that the tactile feedback is not as good as many users would like. Although it is reasonable for most, some users prefer more tactile feedback than rubber dome keyboards normally provide.

The membrane keyboard is a variation on the rubber dome type in which the keys themselves are no longer separate, but are formed together in a sheet that sits on the rubber dome sheet. This severely limits key travel, and membrane keyboards are not considered usable for normal touch typing because of this. They are ideal in extremely harsh environments. Because the sheets can be bonded together and sealed from the elements, membrane keyboards can be used in situations in which no other type could survive. Many industrial applications use membrane keyboards especially for terminals that do not require extensive data entry but are used to operate equipment such as cash registers.

Capacitive switches are the only nonmechanical type of switch in use today (see Figure 9.6). These are the Cadillac of key switches. They are much more expensive than the more common mechanical rubber dome, but they also are more resistant to dirt and corrosion and offer the highest-quality tactile feedback of any type of switch.

A capacitive switch does not work by making contact between conductors. Instead, two plates usually made of plastic are connected in a switch matrix designed to detect changes in the capacitance of the circuit.

When the key is pressed, the plunger moves the top plate relative to the fixed bottom plate. Usually a mechanism provides for a distinct over-center tactile feedback with a resounding "click." As the top plate moves, the capacitance between the two plates changes and is detected by the comparator circuitry in the keyboard.

FIG. 9.6 A capacitive key switch.

Because this type of switch does not rely on metal contacts, it is nearly immune to corrosion and dirt. These switches are very resistant to key bounce problems that result in multiple characters appearing from a single strike. They are also the most durable in the industry--rated for 25 million or more keystrokes, as opposed to 10 to 20 million for other designs. The tactile feedback is unsurpassed because a relatively loud click and strong over-center feel normally are provided. The only drawback to this design is the cost. Capacitive switch keyboards are among the most expensive designs, but the quality of the feel and their durability are worth it.

Traditionally, the only vendors of capacitive key switch keyboards have been IBM and its keyboard division, Lexmark, which is why these keyboards have always seemed to stand out as superior from the rest.

The Keyboard Interface

A keyboard consists of a set of switches mounted in a grid or array called the key matrix. When a switch is pressed, a processor in the keyboard itself identifies which key is pressed by identifying which grid location in the matrix shows continuity. The keyboard processor also interprets how long the key is pressed and can even handle multiple keypresses at the same time. A 16-byte hardware buffer in the keyboard can handle rapid or multiple keypresses, passing each one in succession to the system.

When you press a key, in most cases the contact actually bounces slightly, meaning that there are several rapid on-off cycles just as the switch makes contact. This is called bounce, and the processor in the keyboard is designed to filter this, or debounce the keystroke. The keyboard processor must distinguish bounce from a double keystrike actually intended by the keyboard operator. This is fairly easy because the bouncing is much more rapid than a person could simulate by striking a key quickly several times.

The keyboard in an PC-compatible system is actually a computer itself. It communicates with the main system through a special serial data link that transmits and receives data in 11-bit packets of information consisting of 8 data bits in addition to framing and control bits. Although it is indeed a serial link (the data flows on one wire), it is not compatible with the standard RS-232 serial port commonly used to connect modems.

The processor in the original PC keyboard was an Intel 8048 microcontroller chip. Newer keyboards often use an 8049 version that has built-in ROM or other microcontroller chips compatible with the 8048 or 8049. For example, in its enhanced keyboards, IBM has always used a custom version of the Motorola 6805 processor, which is compatible with the Intel chips. The keyboard's built-in processor reads the key matrix, debounces the keypress signals, converts the keypress to the appropriate scan code, and transmits the code to the motherboard. The processors built into the keyboard contain their own RAM, possibly some ROM, and a built-in serial interface.

In the original PC/XT design, the keyboard serial interface is connected to an 8255 Programmable Peripheral Interface (PPI) chip on the motherboard of the PC/XT. This chip is connected to the interrupt controller IRQ1 line, which is used to signal that keyboard data is available. The data itself is sent from the 8255 to the processor via I/O port address 60h. The IRQ1 signal causes the main system processor to run a subroutine (`INT 9h`) that interprets the keyboard scan code data and decides what to do.

In an AT-type keyboard design, the keyboard serial interface is connected to a special keyboard controller on the motherboard. This is an Intel 8042 Universal Peripheral Interface (UPI) slave microcontroller chip in the original AT design. This microcontroller is essentially another processor that has its own 2K of ROM and 128 bytes of RAM. An 8742 version that uses EPROM (Erasable Programmable Read Only Memory) can be erased and reprogrammed. Often when you get a motherboard ROM upgrade from a motherboard manufacturer, it includes a new keyboard controller chip because it has somewhat dependent and updated ROM code in it as well. Some systems may use the 8041 or 8741 chips, which differ only in the amount of ROM or RAM built in, whereas other systems now have the keyboard controller built into the main system chipset.

In an AT system, the (8048-type) microcontroller in the keyboard sends data to the (8042-type) motherboard keyboard controller on the motherboard. The motherboard-based controller can also send data back to the keyboard. When the keyboard controller on the motherboard receives data from the keyboard, it signals the motherboard with an IRQ1 and sends the data to the main motherboard processor via I/O port address 60h, just as in the PC/XT. Acting as an agent between the keyboard and the main system processor, the 8042-type keyboard controller can translate scan codes and perform several other functions as well. Data also can be sent to the 8042 keyboard controller via port 60h, which is then passed on to the keyboard. Additionally, when the system needs to send commands to or read the status of the keyboard controller on the motherboard, it reads or writes through I/O port 64h. These commands are also usually followed by data sent back and forth via port 60h.

In most older systems the 8042 keyboard controller is also used by the system to control the A20 memory address line, which controls access to system memory greater than 1M. More modern motherboards usually incorporate this functionality directly in the motherboard chipset. This aspect of the keyboard controller is discussed in Chapter 7, "Memory," in the section that covers the High Memory Area (HMA).

Typematic Functions

If a key on the keyboard is held down, it becomes typematic, which means that the keyboard repeatedly sends the keypress code to the motherboard. In the AT-style keyboards, the typematic rate is adjustable by sending the keyboard processor the appropriate commands. This is not possible for the earlier PC/XT keyboard types because the keyboard interface is not bi-directional.

AT-style keyboards have a programmable typematic repeat rate and delay parameter. The DOS `MODE` command in versions 4.0 and later enables you to set the keyboard typematic (repeat) rate as well as the delay before typematic action begins. The default value for the `RATE` parameter (r) is 20 for PC-compatible systems and 21 for IBM PS/2 systems. The default value for the `DELAY` parameter is 2. Thus for most systems, the standard keyboard typematic speed is 10cps (characters per second), and the delay before typematic action occurs is 0.5 seconds.

To use the DOS `MODE` command to reset the keyboard typematic rate and delay, use the following command:

    MODE CON[:] [RATE=r DELAY=d]

The acceptable values for the rate r and the resultant typematic rate in cps are shown in Table 9.1.

#### Table 9.1 DOS 4.0+ MODE Command Keyboard Typematic Rate Parameters

Rate No. | Rate ± 20% | Rate No. | Rate ± 20%
32 | 30.0cps | 16 | 7.5cps
31 | 26.7cps | 15 | 6.7cps
30 | 24.0cps | 14 | 6.0cps
29 | 21.8cps | 13 | 5.5cps
28 | 20.0cps | 12 | 5.0cps
27 | 18.5cps | 11 | 4.6cps
26 | 17.1cps | 10 | 4.3cps
25 | 16.0cps | 9 | 4.0cps
24 | 15.0cps | 8 | 3.7cps
23 | 13.3cps | 7 | 3.3cps
22 | 12.0cps | 6 | 3.0cps
21 | 10.9cps | 5 | 2.7cps
20 | 10.0cps | 4 | 2.5cps
19 | 9.2cps | 3 | 2.3cps
18 | 8.6cps | 2 | 2.1cps
17 | 8.0cps | 1 | 2.0cps

Table 9.2 shows the values for `DELAY` and the resultant delay time in seconds.

#### Table 9.2 DOS MODE Command Keyboard Typematic Delay Parameters

DELAY No. | Delay Time
1 | 0.25sec
2 | 0.50sec
3 | 0.75sec
4 | 1.00sec

For example, I always place the following command in my AUTOEXEC.BAT file:

    MODE CON: RATE=32 DELAY=1

This command sets the typematic rate to the maximum speed possible, or 30cps. It also trims the delay to the minimum of 0.25 seconds before repeating begins. This command "turbocharges" the keyboard and makes operations requiring repeated keystrokes work much faster, such as moving within a file using arrow keys. The quick typematic action and short delay can sometimes be disconcerting to ham-fisted keyboard operators. In that case, slow typists might want to leave their keyboard speed at the default until they become more proficient.

> NOTE: If you have an older system or keyboard, you may receive the following message:

>     Function not supported on this computer

> This indicates that your system, keyboard, or both do not support the bi-directional interface or commands required to change the typematic rate and delay. Upgrading the BIOS or the keyboard may enable this function, but it is probably not cost-effective to do this on an older system.

> NOTE: Many BIOS versions feature keyboard speed selection capability; however, not all of them allow full control over the speed and delay.

Windows maintains its own independent settings for the keyboard typematic rate and delay. This means that even if you use the `MODE` command to set them in DOS, when Windows is loaded it will override any previous settings. Fortunately, the keyboard typematic rate and delay can easily be viewed or changed from within Windows. To do this, first open the Control Panel, then select the Keyboard icon where you will see the repeat rate and delay settings. If you want to adjust the typematic rate, drag the Repeat Rate slider to the desired setting. If you want to adjust the time delay before repeating occurs, drag the Repeat Delay slider to the desired setting. You can test the repeat delay and repeat rate by clicking the box below the sliders and then holding down a key.

Keyboard Key Numbers and Scan Codes

When you press a key on the keyboard, the processor built into the keyboard (8048- or 6805-type) reads the keyswitch location in the keyboard matrix. The processor then sends to the motherboard a serial packet of data that contains the scan code for the key that was pressed. In AT-type motherboards that use an 8042-type keyboard controller, the 8042 chip translates the actual keyboard scan code into one of up to three different sets of system scan codes, which are sent to the main processor. It can be useful in some cases to know what these scan codes are, especially when troubleshooting keyboard problems or when reading the keyboard or system scan codes directly in software.

When a keyswitch on the keyboard sticks or otherwise fails, the scan code of the failed keyswitch is usually reported by diagnostics software, including the POST (Power On Self-Test), as well as conventional disk-based diagnostics. This means that you have to identify the particular key by its scan code. Tables 9.3 through 9.7 list all the scan codes for every key on the 83-, 84-, and 101-key keyboards. By looking up the reported scan code on these charts, you can determine which keyswitch is defective or needs to be cleaned.

> NOTE: 101-key enhanced keyboards are capable of three different scan code sets. Set 1 is the default. Some systems, including some of the PS/2 machines, use one of the other scan code sets during the POST. For example, the IBM P75 I have uses Scan Code Set 2 during the POST but switches to Set 1 during normal operation. This is rare and really threw me off in diagnosing a stuck key problem at one time, but it is useful to know if you are having difficulty interpreting the Scan Code number.

IBM also assigns each key a unique key number to distinguish it from the others. This is important when you are trying to identify keys on foreign keyboards, which may use different symbols or characters from the U.S. models. In the case of the enhanced keyboard, most foreign models are missing one of the keys (key 29) found on the U.S. version and have two other additional keys (keys 42 and 45) as well. This accounts for the 102-key total rather than the 101-keys found on the U.S. version.

Figure 9.7 shows the keyboard numbering and character locations for the original 83-key PC keyboard. Table 9.3 shows the scan codes for each key relative to the key number and character.

FIG. 9.7 83-key PC keyboard key number and character locations.

#### Table 9.3 83-Key (PC/XT) Keyboard Key Numbers and Scan Codes

Key Number | Scan Code | Key
1 | 01 | Esc
2 | 02 | 1
3 | 03 | 2
4 | 04 | 3
5 | 05 | 4
6 | 06 | 5
7 | 07 | 6
8 | 08 | 7
9 | 09 | 8
10 | 0A | 9
11 | 0B | 0
12 | 0C | -
13 | 0D | =
14 | 0E | Backspace
15 | 0F | Tab
16 | 10 | q
17 | 11 | w
18 | 12 | e
19 | 13 | r
20 | 14 | t
21 | 15 | y
22 | 16 | u
23 | 17 | i
24 | 18 | o
25 | 19 | p
26 | 1A | [
27 | 1B | ]
28 | 1C | Enter
29 | 1D | Ctrl
30 | 1E | a
31 | 1F | s
32 | 20 | d
33 | 21 | f
34 | 22 | g
35 | 23 | h
36 | 24 | j
37 | 25 | k
38 | 26 | l
39 | 27 | ;
40 | 28 | `
41 | 29 | `
42 | 2A | Left Shift
43 | 2B | \
44 | 2C | z
45 | 2D | x
46 | 2E | c
47 | 2F | v
48 | 30 | b
49 | 31 | n
50 | 32 | m
51 | 33 | ,
52 | 34 | .
53 | 35 | /
54 | 36 | Right Shift
55 | 37 | *
56 | 38 | Alt
57 | 39 | Space bar
58 | 3A | Caps Lock
59 | 3B | F1
60 | 3C | F2
61 | 3D | F3
62 | 3E | F4
63 | 3F | F5
64 | 40 | F6
65 | 41 | F7
66 | 42 | F8
67 | 43 | F9
68 | 44 | F10
69 | 45 | Num Lock
70 | 46 | Scroll Lock
71 | 47 | Keypad 7 (Home)
72 | 48 | Keypad 8 (Up arrow)
73 | 49 | Keypad 9 (PgUp)
74 | 4A | Keypad -
75 | 4B | Keypad 4 (Left arrow)
76 | 4C | Keypad 5
77 | 4D | Keypad 6 (Right arrow)
78 | 4E | Keypad +
79 | 4F | Keypad 1 (End)
80 | 50 | Keypad 2 (Down arrow)

Figure 9.8 shows the keyboard numbering and character locations for the original 84-key AT keyboard. Table 9.4 shows the scan codes for each key relative to the key number and character.

FIG. 9.8 84-key AT keyboard key number and character locations.

#### Table 9.4 84-Key AT Keyboard Key Numbers and Scan Codes

Key Number | Scan Code | Key
1 | 29 | `
2 | 02 | 1
3 | 03 | 2
4 | 04 | 3
5 | 05 | 4
6 | 06 | 5
7 | 07 | 6
8 | 08 | 7
9 | 09 | 8
10 | 0A | 9
11 | 0B | 0
12 | 0C | -
13 | 0D | =
14 | 2B | \
15 | 0E | Backspace
16 | 0F | Tab
17 | 10 | q
18 | 11 | w
19 | 12 | e
20 | 13 | r
43 | 1C | Enter
44 | 2A | Left Shift
46 | 2C | z
47 | 2D | x
48 | 2E | c
49 | 2F | v
50 | 30 | b
51 | 31 | n
52 | 32 | m
53 | 33 | ,
54 | 34 | .
55 | 35 | /
57 | 36 | Right Shift
58 | 38 | Alt
61 | 39 | Space bar
64 | 3A | Caps Lock
65 | 3C | F2
66 | 3E | F4
67 | 40 | F6
68 | 42 | F8
69 | 44 | F10
70 | 3B | F1
71 | 3D | F3
72 | 3F | F5
73 | 41 | F7
74 | 43 | F9
90 | 01 | Escape
91 | 47 | Keypad 7 (Home)
92 | 4B | Keypad 4 (Left arrow)
93 | 4F | Keypad 1 (End)
95 | 45 | Num Lock
96 | 48 | Keypad 8 (Up arrow)
97 | 4C | Keypad 5
98 | 50 | Keypad 2 (Down arrow)
99 | 52 | Keypad 0 (Ins)
100 | 46 | Scroll Lock
101 | 49 | Keypad 9 (PgUp)
102 | 4D | Keypad 6 (Right arrow)
103 | 51 | Keypad 3 (PgDn)
104 | 53 | Keypad . (Del)
105 | 54 | SysRq
106 | 37 | Keypad *
107 | 4A | Keypad -
108 | 4E | Keypad +

Figure 9.9 shows the keyboard numbering and character locations for the 101-key enhanced keyboard. Tables 9.5 through 9.8 show each of the three scan code sets for each key relative to the key number and character. Scan Code Set 1 is the default; the other two are rarely used. Figure 9.10 shows the layout of a typical foreign language 102-key version of the enhanced keyboard--in this case, a U.K. version.

FIG. 9.9 101-key enhanced keyboard key number and character locations (U.S. version).

FIG. 9.10 102-key enhanced keyboard key number and character locations (U.K. English version).

#### Table 9.5 101/102-Key (Enhanced) Keyboard Key Numbers and Scan
Codes (Set 1)

Key Number | Scan Code | Key
1 | 29 | `
2 | 02 | 1
3 | 03 | 2
4 | 04 | 3
5 | 05 | 4
6 | 06 | 5
7 | 07 | 6
8 | 08 | 7
9 | 09 | 8
10 | 0A | 9
11 | 0B | 0
12 | 0C | -
13 | 0D | =
15 | 0E | Backspace
16 | 0F | Tab
17 | 10 | q
18 | 11 | w
19 | 12 | e
20 | 13 | r
21 | 14 | t
22 | 15 | y
23 | 16 | u
24 | 17 | i
25 | 18 | o
26 | 19 | p
27 | 1A | [
28 | 1B | ]
29 | 2B | \ (101-key only)
30 | 3A | Caps Lock
31 | 1E | a
32 | 1F | s
33 | 20 | d
34 | 21 | f
35 | 22 | g
36 | 23 | h
37 | 24 | j
38 | 25 | k
39 | 26 | l
40 | 27 | ;
41 | 28 | `
42 | 2B | # (102-key only)
43 | 1C | Enter
44 | 2A | Left Shift
45 | 56 | \ (102-key only)
46 | 2C | z
47 | 2D | x
48 | 2E | c
49 | 2F | v
50 | 30 | b
51 | 31 | n
52 | 32 | m
53 | 33 | ,
54 | 34 | .
55 | 35 | /
57 | 36 | Right Shift
58 | 1D | Left Ctrl
60 | 38 | Left Alt
61 | 39 | Space bar
62 | E0,38 | Right Alt
64 | E0,1D | Right Ctrl
75 | E0,52 | Insert
76 | E0,53 | Delete
79 | E0,4B | Left arrow
80 | E0,47 | Home
81 | E0,4F | End
83 | E0,48 | Up arrow
84 | E0,50 | Down arrow
85 | E0,49 | Page Up
86 | E0,51 | Page Down
89 | E0,4D | Right arrow
90 | 45 | Num Lock
91 | 47 | Keypad 7 (Home)
92 | 4B | Keypad 4 (Left arrow)
93 | 4F | Keypad 1 (End)
95 | E0,35 | Keypad /
96 | 48 | Keypad 8 (Up arrow)
97 | 4C | Keypad 5
98 | 50 | Keypad 2 (Down arrow)
99 | 52 | Keypad 0 (Ins)
100 | 37 | Keypad *
101 | 49 | Keypad 9 (PgUp)
102 | 4D | Keypad 6 (Left arrow)
103 | 51 | Keypad 3 (PgDn)
104 | 53 | Keypad . (Del)
105 | 4A | Keypad -
106 | 4E | Keypad +
108 | E0,1C | Keypad Enter
110 | 01 | Escape
112 | 3B | F1
113 | 3C | F2
114 | 3D | F3
115 | 3E | F4
116 | 3F | F5
117 | 40 | F6
118 | 41 | F7
119 | 42 | F8
120 | 43 | F9
121 | 44 | F10
122 | 57 | F11
123 | 58 | F12
124 | E0,2A, E0,37 | Print Screen
125 | 46 | Scroll Lock
126 | E1,1D,45, E1,9D,C5 | Pause

#### Table 9.6 101/102-Key (Enhanced) Keyboard Key Numbers and Scan
Codes (Set 2)

Key Number | Scan Code | Key
1 | 0E | `
2 | 16 | 1
3 | 1E | 2
4 | 26 | 3
5 | 25 | 4
6 | 2E | 5
7 | 36 | 6
8 | 3D | 7
9 | 3E | 8
10 | 46 | 9
11 | 45 | 0
12 | 4E | -
13 | 55 | =
15 | 66 | Backspace
16 | 0D | Tab
17 | 15 | q
18 | 1D | w
19 | 24 | e
20 | 2D | r
21 | 2C | t
22 | 35 | y
23 | 3C | u
24 | 43 | i
25 | 44 | o
26 | 4D | p
27 | 54 | [
28 | 5B | ]
29 | 5D | \ (101-key only)
30 | 58 | Caps Lock
31 | 1C | a
32 | 1B | s
33 | 23 | d
34 | 2B | f
35 | 34 | g
36 | 33 | h
37 | 3B | j
38 | 42 | k
39 | 4B | l
40 | 4C | ;
41 | 52 | `
42 | 5D | # (102-key only)
43 | 5A | Enter
44 | 12 | Left Shift
45 | 61 | \ (102-key only)
46 | 1A | z
47 | 22 | x
48 | 21 | c
49 | 2A | v
50 | 32 | b
51 | 31 | n
52 | 3A | m
53 | 41 | ,
54 | 49 | .
55 | 4A | /
57 | 59 | Right Shift
58 | 14 | Left Ctrl
60 | 11 | Left Alt
61 | 29 | Space bar
62 | E0,11 | Right Alt
64 | E0,14 | Right Ctrl
75 | E0,70 | Insert
76 | E0,71 | Delete
79 | E0,6B | Left arrow
80 | E0,6C | Home
81 | E0,69 | End
83 | E0,75 | Up arrow
84 | E0,72 | Down arrow
85 | E0,7D | Page Up
86 | E0,7A | Page Down
89 | E0,74 | Right arrow
90 | 77 | Num Lock
91 | 6C | Keypad 7 (Home)
92 | 6B | Keypad 4 (Left arrow)
93 | 69 | Keypad 1 (End)
95 | E0,4A | Keypad /
96 | 75 | Keypad 8 (Up arrow)
97 | 73 | Keypad 5
98 | 72 | Keypad 2 (Down arrow)
99 | 70 | Keypad 0 (Ins)
100 | 7C | Keypad *
101 | 7D | Keypad 9 (PgUp)
102 | 74 | Keypad 6 (Left arrow)
103 | 7A | Keypad 3 (PgDn)
104 | 71 | Keypad . (Del)
105 | 7B | Keypad -
106 | E0,5A | Keypad +
108 | E0,5A | Keypad Enter
110 | 76 | Escape
112 | 05 | F1
113 | 06 | F2
114 | 04 | F3
115 | 0C | F4
116 | 03 | F5
117 | 0B | F6
118 | 83 | F7
119 | 0A | F8
120 | 01 | F9
121 | 09 | F10
122 | 78 | F11
123 | 07 | F12
124 | E0,12,E0,7C | Print Screen
125 | 7E | Scroll Lock
126 | E1,14,77,E1, F0,14,F0,77 | Pause

#### Table 9.7 101/102-Key (Enhanced) Keyboard Key Numbers and Scan
Codes (Set 3)

Key Number | Scan Code | Key
1 | 0E | `
2 | 16 | 1
3 | 1E | 2
4 | 26 | 3
5 | 25 | 4
6 | 2E | 5
7 | 36 | 6
8 | 3D | 7
9 | 3E | 8
10 | 46 | 9
11 | 45 | 0
12 | 4E | -
13 | 55 | =
15 | 66 | Backspace
16 | 0D | Tab
17 | 15 | q
18 | 1D | w
19 | 24 | e
20 | 2D | r
21 | 2C | t
22 | 35 | y
23 | 3C | u
24 | 43 | i
25 | 44 | o
26 | 4D | p
27 | 54 | [
28 | 5B | ]
29 | 5C | \ (101-key only)
30 | 14 | Caps Lock
31 | 1C | a
32 | 1B | s
33 | 23 | d
34 | 2B | f
35 | 34 | g
36 | 33 | h
37 | 3B | j
38 | 42 | k
39 | 4B | l
40 | 4C | ;
41 | 52 | `
42 | 53 | # (102-key only)
43 | 5A | Enter
44 | 12 | Left Shift
45 | 13 | \ (102-key only)
46 | 1A | z
47 | 22 | x
48 | 21 | c
49 | 2A | v
50 | 32 | b
51 | 31 | n
52 | 3A | m
53 | 41 | ,
54 | 49 | .
55 | 4A | /
57 | 59 | Right Shift
58 | 11 | Left Ctrl
60 | 19 | Left Alt
61 | 29 | Space bar
62 | 39 | Right Alt
64 | 58 | Right Ctrl
75 | 67 | Insert
76 | 64 | Delete
79 | 61 | Left arrow
80 | 6E | Home
81 | 65 | End
83 | 63 | Up arrow
84 | 60 | Down arrow
85 | 6F | Page Up
86 | 6D | Page Down
89 | 6A | Right arrow
90 | 76 | Num Lock
91 | 6C | Keypad 7 (Home)
92 | 6B | Keypad 4 (Left arrow)
93 | 69 | Keypad 1 (End)
95 | 77 | Keypad /
96 | 75 | Keypad 8 (Up arrow)
97 | 73 | Keypad 5
98 | 72 | Keypad 2 (Down arrow)
99 | 70 | Keypad 0 (Ins)
100 | 7E | Keypad *
101 | 7D | Keypad 9 (PgUp)
102 | 74 | Keypad 6 (Left arrow)
103 | 7A | Keypad 3 (PgDn)
104 | 71 | Keypad . (Del)
105 | 84 | Keypad -
106 | 7C | Keypad +
108 | 79 | Keypad Enter
110 | 08 | Escape
112 | 07 | F1
113 | 0F | F2
114 | 17 | F3
115 | 1F | F4
116 | 27 | F5
117 | 2F | F6
118 | 37 | F7
119 | 3F | F8
120 | 47 | F9
121 | 4F | F10
122 | 56 | F11
123 | 5E | F12
124 | 57 | Print Screen
125 | 5F | Scroll Lock
126 | 62 | Pause

The new keys found on a 104-key Windows keyboard have their own unique scan codes. Table 9.8 shows the scan codes for the new keys.

#### Table 9.8 104-Key Windows Keyboard New Key Scan Codes

New Key | Scan Code Set 1 | Scan Code Set 2 | Scan Code Set 3
Left Windows | E0,5B | E0,1F | 8B
Right Windows | E0,5C | E0,27 | 8C
Application | E0,5D | E0,2F | 8D

Knowing these key number figures and scan codes is useful when you are troubleshooting stuck or failed keys on a keyboard. Diagnostics can report the defective keyswitch by the scan code, which varies from keyboard to keyboard as to the character it represents and its location.

Keyboard/Mouse Interface Connectors

Keyboards have a cable available with one of two primary types of connectors at the system end. Most aftermarket keyboards have a cable connected inside the keyboard case on the keyboard end and require that you open up the keyboard case to disconnect or test. Actual IBM enhanced keyboards use a unique cable assembly that plugs into both the keyboard as well as the system unit. This makes cable interchange or replacement an easy plug-in affair. A special connector called an SDL (Shielded Data Link) is used at the keyboard end and the appropriate DIN connector at the PC end. Any IBM keyboard or cable can be ordered separately as a spare part. The newer enhanced keyboards come with an externally detachable keyboard cable that plugs into the keyboard port with a special connector, much like a telephone connector. The other end of the cable is one of the following two types:

- 5-pin DIN connector. Used on most PC-compatible systems with Baby-AT form factor motherboards.
- 6-pin mini-DIN connector. Used on PS/2 systems and most Low Profile (LPX motherboard) PC compatibles.

Figure 9.11 and Table 9.9 show the physical layout and pinouts of all the respective keyboard connector plugs and sockets.

#### Table 9.9 Keyboard Connector Signals

Signal Name | 5-Pin DIN | 6-Pin Mini-DIN | 6-Pin SDL
Keyboard Data | 2 | 1 | B
Ground | 4 | 3 | C
+5v | 5 | 4 | E
Keyboard Clock | 1 | 5 | D
Not Connected | -- | 2 | A
Not Connected | -- | 6 | F
Not Connected | 3 | -- | --

DIN = German Industrial Norm (Deutsche Industrie Norm), a committee that sets German dimensional standards

SDL = Shielded Data Link, a type of shielded connector created by AMP and used by IBM and others for keyboard cables

FIG. 9.11 Keyboard and mouse connectors.

Motherboard mouse connectors use the 6-pin mini-DIN connector and have the same pinout and signal descriptions as the keyboard connector; however, the data packets are incompatible. This means that you can easily plug a motherboard mouse (PS/2 style) into a mini-DIN keyboard connector, or plug the mini-DIN type keyboard connector into a motherboard mouse port; however, neither one would work properly in this situation.

Keyboards with Special Features

There are a number of keyboards on the market that have special features not found in the standard designs. These additional features can be simple things such as built-in calculators and clocks, to more complicated features such as integrated pointing devices, special character layouts, shapes, and even programmable keys.

Over the years, many have attempted to change the design of the standard keyboard in an attempt to improve typing speed and ergonomics. Around 1936, August Dvorak and William L. Dealy developed a modified character layout for the keyboard, which replaced the QWERTY layout we are all familiar with today.

The Dvorak-Dealy keyboard design is normally just called the Dvorak design for short. It featured different character positions on the keys designed to promote the alternation of hands during typing. The characters are arranged so that the vowels are in the home row under the left hand, while the consonants used most frequently are placed in the home row under the right hand. The theory was that this would dramatically improve typing speed; however, most tests show fairly modest improvements. The public being resistant to change, the Dvorak keyboard design has not achieved widespread popularity, and the familiar QWERTY layout is still by far the most common design.

A more recent trend is to change the shape of the keyboard instead of altering the character layout. This has resulted in a number of different so-called ergonomic designs. The goal is to shape the keyboard to better fit the human hand. The most common of these designs split the keyboard in the center, bending the sides back. Some allow the angle between the sides to be adjusted, such as with the Lexmark Select-Ease design, while others are fixed, such as the Microsoft Natural keyboard. These split or bent designs more easily conform to the natural angle of the hands while typing. They can improve productivity and typing speed, as well as help prevent medical problems such as Carpal Tunnel Syndrome (tendon inflammation).

Virtually every keyboard company now has some form of similar ergonometric keyboard, and the same things apply with respect to quality and feel as with the standard keyboard designs. The Microsoft Natural Keyboard is manufactured for Microsoft by Keytronics, and uses the inexpensive light-touch keyswitches they are known for. For those who prefer a more rugged keyboard with higher quality switches, I recommend the Lexmark Select-Ease, Alps, NMB Technologies, or Lite-On keyboards. These keyboards are available with very high quality mechanical switches with a positive tactile feel to them. The Lexmark design, in particular, allows you to adjust the angle between the two sides of the keyboard from fully closed like a standard keyboard, to split at virtually any angle. You can even separate the two halves completely. It also features built-in palm rests, an oversized space bar, and cursor keys on both sides of the keyboard.

Although these ergonometric keyboards sound like a good idea, people are resistant to change, and none of these designs has yet to significantly displace the standard keyboard layout.

Several companies including Maxi-Switch have introduced a keyboard that features keys that are programmable. You can assign different keystrokes to keys, or even reprogram the entire keyboard layout. This type of keyboard has been supplied in the past by some of the PC compatible vendors such as Gateway. At one time I used a number of these keyboards in the seminars I teach, and unfortunately I found the programming functions to be difficult to remember; accidentally pressing the programming control keys would often put the keyboard into an altered state requiring it to be reset. One other problem was that the extra keys added width to the keyboard, making it wider than most other standard designs. I quickly decided that the programming functions were so rarely used that they were simply not worth the hassle, and specified standard keyboards for future purchases.

### Keyboard Troubleshooting and Repair

Keyboard errors are usually caused by two simple problems. Other more difficult intermittent problems can arise, but they are also much less likely. The most common problems are:

- Defective cables
- Stuck keys

Defective cables are easy to spot if the failure is not intermittent. If the keyboard stops working altogether or every keystroke results in an error or incorrect character, the cable is likely the culprit. Troubleshooting is simple, especially if you have a spare cable on hand. Simply replace the suspected cable with one from a known working keyboard, and verify whether the problem still exists. If it does, the problem must be elsewhere. You also can test the cable for continuity with it removed from the keyboard by using a DMM (Digital Multi-Meter). DMMs that have an audible continuity tester built in make this procedure much easier to perform. Wiggle the ends of the cable as you check each wire to make sure that there are no intermittent connections. If you discover a problem with the continuity in one of the wires, replace the cable or the entire keyboard, if that is cheaper. Because replacement keyboards are so inexpensive, sometimes it can be cheaper to replace the entire unit than to get a new cable.

Many times you first discover a problem with a keyboard because the system has an error during the POST. Most systems use error codes in a 3xx numeric format to distinguish the keyboard. If you have any such errors during the POST, write them down. Some BIOS versions do not use cryptic numeric error codes and simply state something like the following:

    Keyboard stuck key failure

This message normally would be displayed by a system with a Phoenix BIOS if a key were stuck. Unfortunately, that message does not identify which key it is!

If your 3xx (keyboard) error is preceded by a two-digit hexadecimal number, this number is the scan code of a failing or stuck keyswitch. Look up the scan code in the tables provided in this section to determine which keyswitch is the culprit. These charts tell you to which key the scan code refers. By removing the keycap of the offending key and cleaning the switch, you can often solve the problem.

For a simple test of the motherboard keyboard connector, you can check voltages on some of the pins. Use Figure 9.10 in the preceding section as a guide, and measure the voltages on various pins of the keyboard connector. To prevent possible damage to the system or keyboard, first turn off the power before disconnecting the keyboard. Then unplug the keyboard, and turn the power back on. Make measurements between the ground pin and the other pins according to Table 9.10. If the voltages are within these specifications, the motherboard keyboard circuitry is probably okay.

#### Table 9.10 Keyboard Connector Specifications

DIN Connector Pin | Mini-DIN Pin | Signal | Connector Voltage
1 | 5 | Keyboard Clock | +2.0v to +5.5v
2 | 1 | Keyboard Data | +4.8v to +5.5v
3 | - | Reserved | --
4 | 3 | Ground | --
5 | 4 | +5v Power | +2.0v to +5.5v

If your measurements do not match these voltages, the motherboard might be defective. Otherwise, the keyboard cable or keyboard might be defective. If you suspect that the cable is the problem, the easiest thing to do is to replace the keyboard cable with a known good one. If the system still does not work normally, you may have to replace either the entire keyboard or the motherboard.

In many newer systems, the motherboard keyboard and mouse connectors are protected by a fuse that can be replaced. Look for any type of fuse on the motherboard in the vicinity of the keyboard or mouse connectors. Other systems may have a socketed keyboard controller chip (8042-type). In that case, it may be possible to repair the motherboard keyboard circuit by replacing this chip. Because these chips have ROM code in them, it is best to get the replacement from the motherboard or BIOS manufacturer.

Here is a list of standard POST and diagnostics keyboard error codes:

Error Code | Description
3xx | Keyboard errors.
301 | Keyboard reset or stuck-key failure (XX 301, XX = scan code in hex).
302 | System unit keylock switch is locked.
302 | User-indicated keyboard test error.
303 | Keyboard or system-board error; keyboard controller failure.
304 | Keyboard or system-board error; keyboard clock high.
305 | Keyboard +5v error; PS/2 keyboard fuse (on motherboard) blown.
341 | Keyboard error.
342 | Keyboard cable error.
343 | Keyboard LED card or cable failure.
365 | Keyboard LED card or cable failure.
366 | Keyboard interface cable failure.
367 | Keyboard LED card or cable failure.

Disassembly Procedures and Cautions

Repairing and cleaning a keyboard often requires you to take it apart. When performing this task, you must know when to stop! Some keyboards literally come apart into hundreds of little pieces that are almost impossible to reassemble if you go too far. An IBM keyboard generally has these four major parts:

- Cable Keypad assembly
- Case Keycaps

You easily can break down a keyboard to these major components and replace any of them, but don't disassemble the keypad assembly or you will be showered with hundreds of tiny springs, clips, and keycaps. Finding all these parts--several hundred of them--and piecing the unit back together is not a fun way to spend your time. You also may not be able to reassemble the keyboard properly. Figure 9.12 shows a typical keyboard with the case opened.

FIG. 9.12 Typical keyboard components.

Another problem is that you cannot purchase the smaller parts separately, such as contact clips and springs. The only way to obtain these parts is from another keyboard. If you ever have a keyboard that is beyond repair, keep it around for these parts. They might come in handy some day.

Most repair operations are limited to changing the cable or cleaning some component of the keyboard, from the cable contact ends to the key contact points. The keyboard cable takes quite a lot of abuse and, therefore, can fail easily. The ends are stretched, tugged, pulled, and generally handled roughly. The cable uses strain reliefs, but you still might have problems with the connectors making proper contact at each end or even with wires that have broken inside the cable. You might want to carry a spare cable for every type of keyboard you have.

All keyboard cables plug into the keyboard and PC with connectors, and you can change the cables easily without having to splice wires or solder connections. With the earlier 83-key PC and 84-key AT keyboards, you must open the case to access the connector to which the cable attaches. On the newer 101-key enhanced keyboards from IBM and Lexmark, the cable plugs into the keyboard from the outside of the case, using a modular jack and plug similar to a telephone jack. This design also makes the IBM/Lexmark keyboards universally usable on nearly any system (except the original PC) by easily switching the cable.

The only difference, for example, between the enhanced keyboards for an IBM AT and an IBM PS/2 system is the attached cable. PS/2 systems use a tan cable with a smaller plug on the computer side. The AT cable is black and has the larger DIN-type plug on the computer side. You can interchange the enhanced keyboards as long as you use the correct cable for the system.

The only feasible way to repair a keyboard is to replace the cable and to clean the individual keyswitch assemblies, the entire keypad, or the cable contact ends. The individual spring and keyswitch assemblies are not available as a separate part, and disassembling the unit to that level is not advisable because of the difficulty in reassembling it. Other than cleaning a keyboard, the only thing that you can do is replace the entire keypad assembly (virtually the entire keyboard) or the cable.

Cleaning a Keyboard

One of the best ways to maintain a keyboard in top condition is periodic cleaning. As preventive maintenance, you should vacuum the keyboard weekly or at least monthly. You can also use canned compressed air (available at electronics supply houses) to blow the dust and dirt out instead of using a vacuum. Before you dust a keyboard with the compressed air, turn the keyboard upside down so that the particles of dirt and dust collected inside can fall out.

On all keyboards, each keycap is removable, which can be handy if a key sticks or acts erratically. For example, a common problem is a key that does not work every time you press it. This problem usually results from dirt collecting under the key. An excellent tool for removing keycaps on most any keyboard is the U-shaped chip-puller tool. Simply slip the hooked ends of the tool under the keycap, squeeze the ends together to grip the underside of the keycap, and lift up. IBM sells a tool designed specifically for removing keycaps from its keyboards, but the chip puller works even better. After removing the cap, spray some compressed air into the space under the cap to dislodge the dirt. Then replace the cap and check the action of the key.

> CAUTION: When you remove the keycaps, be careful not to remove the space bar on the original 83-key PC and 84-key AT-type keyboards. This bar is very difficult to reinstall. The newer 101-key units use a different wire support that can be removed and replaced much more easily.

Spills also can be a problem. If you tip a soft drink or cup of coffee into a keyboard, you do not necessarily have a disaster. You should immediately (or as soon as possible) flush out the keyboard with distilled water. Partially disassemble the keyboard and use the water to wash the components. (See the following section for disassembly instructions.) If the spilled liquid has dried, soak the keyboard in some of the water for a while. When you are sure that the keyboard is clean, pour another gallon or so of distilled water over it and through the key switches to wash away any residual dirt. After the unit dries completely, it should be perfectly functional. You may be surprised to know that you can drench your keyboard with water, and it will not harm the components. Just make sure that you use distilled water, which is free from residue or mineral content. Also make sure that the keyboard is fully dry before you attempt to use it, or some of the components might short out.

Replacement Keyboards

In most cases, it is cheaper or more cost-effective to replace a keyboard rather than to repair it. This is especially true if the keyboard has an internal malfunction or if one of the keyswitches is defective. Replacement parts for keyboards are almost impossible to procure, and in most cases the installation of any repair part is difficult. In addition, many of the keyboards supplied with lower cost compatible machines leave much to be desired. They often have a mushy feel, with little or no tactile feedback. A poor keyboard can make using a system a frustrating experience, especially if you are a touch typist. For all these reasons, it is often a good idea to replace an existing keyboard with something better.

Perhaps the highest quality keyboards in the entire computer industry are those made by IBM, or more accurately Lexmark. Several years ago, IBM spun off its keyboard and printer divisions as a separate company called Lexmark. Lexmark used to manufacturer most IBM brand keyboards and printers and sells them not only to IBM but also to compatible vendors and end users. This means that if you are lucky, your compatible system comes with a Lexmark keyboard, but if not you can purchase one separately on your own.

Table 9.11 shows the part numbers of all IBM-labeled keyboards and cables. These numbers can serve as a reference when you are seeking a replacement IBM keyboard from IBM directly or from third-party companies. Many third-party companies sell IBM label keyboards for much less than IBM, in both new and refurbished form. Remember that you can also purchase these same keyboards through Lexmark, although they do not come with an IBM label.

#### Table 9.11 IBM Keyboard and Cable Part Numbers

Description | Part Number
83-key U.S. PC Keyboard assembly with cable | 8529297
Cable assembly for 83-key PC Keyboard | 8529168
84-key U.S. AT Keyboard assembly with cable | 8286165
Cable assembly for 84-key keyboard | 8286146
101-key U.S. Keyboard without LED panel | 1390290
101-key U.S. Keyboard with LED panel | 6447033
101-key U.S. Keyboard with LED panel (PS/2 logo) | 1392090
6-foot cable for enhanced keyboard (DIN plug) | 6447051
6-foot cable for enhanced keyboard (mini-DIN plug) | 61X8898
6-foot cable for enhanced keyboard (shielded mini-DIN plug) | 27F4984
10-foot cable for enhanced keyboard (mini-DIN plug) | 72X8537

Notice that the original 83/84-key IBM keyboards are sold with a cable that has the larger, 5-pin DIN connector already attached. IBM enhanced keyboards are always sold (at least by IBM) without a cable. You must order the proper cable as a separate item. Cables are available to connect the keyboards to either the older system units that use the larger DIN connector or to PS/2 systems (and many compatibles) that use the smaller mini-DIN connector.

Recently, IBM has started selling complete keyboard assemblies under a program called IBM Options. This program is designed to sell these components in the retail channel to end users of both IBM and compatible systems from other vendors. Items under the IBM Options program are sold through normal retail channels such as CompUSA, Elek Tek, and Computer Discount Warehouse (CDW). These items are also priced much cheaper than items purchased as spare parts. They include a full warranty and are sold as complete packages including cables. Table 9.12 lists some of the IBM Options keyboards and part numbers.

#### Table 9.12 IBM Options Keyboards (Sold Retail)

Description | Part Number
IBM enhanced keyboard (cable w/DIN plug) | 92G7454
IBM enhanced keyboard (cable w/mini-DIN plug) | 92G7453
IBM enhanced keyboard, built-in trackball (cable w/DIN plug) | 92G7456
IBM enhanced keyboard, built-in trackball (cable w/mini-DIN plug) | 92G7455
IBM enhanced keyboard, integrated trackpoint II (cables w/mini-DIN plugs) | 92G7461

The IBM/Lexmark keyboards use capacitive keyswitches, which are the most durable and lowest maintenance. These switches have no electrical contacts and, instead, rely on changing capacitance to signal a keypress within the switch matrix. This type of design does not have wear points, like a mechanical switch, and has no metal electrical contacts, which makes it virtually immune to the dirt and corrosion problems that plague other designs.

The extremely positive tactile feedback of the IBM/Lexmark design is also a benchmark of comparison for the rest of the industry. Although keyboard feel is an issue of personal preference, I have never used a keyboard that feels better than the IBM/Lexmark designs. I now equip every system I use with a Lexmark keyboard, including the many clone or compatible systems I use. You can purchase these keyboards through Lexmark or a Lexmark distributor for very reasonable prices. You can find IBM-labeled models available from advertisers in Processor or Computer Hotline magazines selling for less than $60.

IBM/Lexmark sells other versions for very reasonable prices as well. Many different models are available, including some with a built-in trackball or even the revolutionary Trackpoint pointing device. Trackpoint refers to a small stick mounted between the G, H, and B keys. This device is an IBM/Lexmark exclusive and was first featured on the IBM Thinkpad laptop systems, although the keyboards are now sold for use on compatibles, and the technology is being licensed to other firms, including Toshiba. Note that this keyboard comes only with the mini-DIN type connectors for both the keyboard and Trackpoint portions, and it works only with a motherboard (PS/2 type) mouse port.

Other high-quality keyboards are available. Several companies, such as Alps, Lite-On, or NMB Technologies, manufacture keyboards similar in feel to the IBM/Lexmark units. They have excellent tactile feedback with a positive click sound. They are my second choice, after a Lexmark unit. Maxi-Switch also makes a high-quality aftermarket keyboard used by a number of compatible manufacturers, including Gateway 2000. These also have a good feel and are recommended. Many of these companies can make their keyboards with your own company logo on them (such as the Maxi-Switch models used by Gateway), which is ideal for clone manufacturers looking for name-brand recognition.

### Reference Material

If you are interested in more details about keyboard design or interfacing, a company called Annabooks publishes a book/disk package called PC Keyboard Design. This document defines the protocol between the keyboard and computer for both XT and AT types and includes schematics and keyboard controller source code. The kit includes a license to use the source code and costs $249.

Other excellent sources of information are the various technical reference manuals put out by IBM. The vendor list contains a list of the important IBM reference manuals in which you can find much valuable information. This information is especially valuable to compatible system manufacturers, because they often do not put out the same level of technical information as IBM, and compatible systems are in many ways similar or even identical to one or more IBM systems. After all, that is why they are called IBM-compatible. Much of my personal knowledge and expertise comes from pouring over the various IBM technical reference manuals.

## Mice

The mouse was invented in 1964 by Douglas Englebart, who at the time was working at the Stanford Research Institute (SRI), a think tank sponsored by Stanford University. The mouse was officially called an X-Y Position Indicator for a Display System. Xerox later applied the mouse to its revolutionary Alto computer system in 1973. At the time, unfortunately, these systems were experimental and used purely for research.

In 1979, several people from Apple, including Steve Jobs, were invited to see the Alto and the software that ran the system. Steve Jobs was blown away by what he saw as the future of computing, which included the use of the mouse as a pointing device and the GUI it operated. Apple promptly incorporated these features into what was to become the Lisa computer and lured away 15 to 20 Xerox scientists to work on the Apple system.

Although Xerox released the Star 8010 computer that used this technology in 1981, it was expensive, poorly marketed, and perhaps way ahead of its time. Apple released the Lisa computer, which was its first system that used the mouse, in 1983. It also was not a runaway success, largely because of its $10,000 list price, but by then Jobs already had Apple working on the low-cost successor to the Lisa, the Macintosh. The Apple Macintosh was introduced in 1984; although it was not an immediate hit, the Macintosh has grown in popularity since that time.

Many credit the Macintosh with inventing the mouse and GUI, but as you can see, this technology was actually borrowed from others, including SRI and Xerox. Certainly the Macintosh, and now Microsoft Windows and OS/2, have gone on to popularize this interface and bring it to the legion of PC-compatible systems.

Although the mouse did not catch on quickly in the PC-compatible marketplace, today the GUIs for PC systems such as Windows and OS/2 virtually demand the use of a mouse. Because of this, it is common for a mouse to be sold with nearly every new system on the market.

Mice come in many shapes and sizes from many different manufacturers. Some have taken the standard mouse design and turned it upside down, creating the trackball. In the trackball devices, you move the ball with your hand directly rather than the unit itself. IBM even produced a very cool mouse/trackball convertible device called the trackpoint (p/n 1397040). The trackpoint could be used as either a mouse (ball side down), or as a track ball (ball side up). In most cases, the dedicated trackballs have a much larger ball than would be found on a standard mouse. Other than the orientation and perhaps the size of the ball, a trackball is identical to a mouse in design, basic function, and electrical interface.

The largest manufacturers of mice are Microsoft and Logitech. Even though mice may come in different varieties, their actual use and care differ very little. The standard mouse consists of several components:

- A housing that you hold in your hand and move around on your desktop
- A roller ball that signals movement to the system
- Buttons (usually two) for making selections
- A cable for connecting the mouse to the system
- An interface connector to attach the mouse to the system

The housing is made of plastic and consists of very few moving parts. On top of the housing, where your fingers normally reside, are buttons. There may be any number of buttons, but in the PC world there are typically only two. If additional buttons are on your mouse, specialized software is required for them to operate. On the bottom of the housing is a small rubber ball that rotates as you move the mouse across the tabletop. The movements of this rubber ball are translated into electrical signals transmitted to the computer across the cable. Some mice use a special optical sensor that detects movement over a grid. These optical mice have fallen into disfavor because they work only if you use a special grid pad underneath them.

The cable can be any length, but is typically between four and six feet long.

> TIP: If you have a choice on the length of cable to purchase, go for a longer one. This allows easier placement of the mouse in relation to your computer.

The connector used with your mouse depends on the type of interface you are using. Three basic interfaces are used, with a fourth combination device possible as well.

After the mouse is connected to your computer, it communicates with your system through the use of a device driver, which can be either separately loaded or built into the system software. For example, no separate drivers are needed to use a mouse with Windows or OS/2, but using the mouse with most DOS-based programs requires a separate driver to be loaded. Regardless of whether it is built in, the driver translates the electrical signals sent from the mouse into positional information and information that indicates the status of the buttons.

Internally, a mouse is very simple as well. The ball usually rests against two rollers, one for translating the X-axis movement and the other for the Y-axis. These rollers are usually connected to small disks with shutters that alternately block and allow the passage of light. Small optical sensors detect movement of the wheels by watching an internal infrared light blink on and off as the shutter wheel rotates and "chops" the light. These blinks are translated into movement along the axes. This type of setup is called an opto-mechanical mechanism and is by far the most popular in use today (see Figure 9.13).

FIG. 9.13 Typical opto-mechanical mouse mechanism.

### Microsoft IntelliMouse

Late in 1996, Microsoft introduced a new variation of its popular mouse, called the IntelliMouse. This device looks exactly like the standard Microsoft mouse except for a miniature gray wheel rising up between the left and right buttons. This wheel represents the only major change in mouse design for many years.

The wheel has two main functions. The primary function is to act as a scrolling device, allowing one to scroll through documents or Web pages by merely pulling down or pushing up with your index finger. It can also function as a third mouse button when you press it.

Although there have been three-button mice available for years, the scrolling function is a real breakthrough. No longer do you have to move the mouse pointer to click the scroll bar on the right hand side of your screen or take your right hand off of the mouse to use the arrow keys on the keyboard; instead, all you have to do is push up or pull down on the wheel! This is a major convenience, especially when browsing Web pages or working with word processing documents or spreadsheets. Also, unlike three-button mice from other vendors, the IntelliMouse's wheel-button doesn't seem to get in the way, and you are less likely to click it by mistake.

One drawback to the IntelliMouse is that the new wheel will only function in software that is rewritten to support it. At the time the IntelliMouse debuted, Microsoft Internet Explorer was already modified to use the new wheel, and all of the applications in Office 97 support it as well. For example, besides just the scrolling capability, most Office 97 applications also allow you to hold down the Ctrl key while turning the wheel to zoom in and out. The wheel and Shift key can also be used to expand and collapse outlines as well. As new and updated versions of other software comes out, you can expect that they will also support the new wheel functions.

The IntelliMouse 2.0 driver combines features from earlier versions of Microsoft's mouse driver with some interesting new functions. A feature called ClickLock allows you to drag items without holding down the left mouse button. You can customize this feature by specifying how long you have to hold the button down to activate ClickLock. The wheel can also be set to scroll a specified number of lines or a screen with each click of the wheel.

You can also set the driver software so that the wheel-button ignores all such application-specific actions and instead performs one of four preset functions in all Windows applications. The four choices are:

- Double-left-click
- Opening an application's help file
- Switching to Windows Explorer
- Bringing up the Start menu

Other driver features retained from earlier versions include a Snap To feature, which moves the pointer to the default button of a dialog box, and a function that adds trails when the pointer moves and also makes the pointer disappear when you start typing.

### Mouse Interface Types

Mice can be connected to your computer through the following three interfaces:

- Serial interface
- Dedicated motherboard mouse port
- Bus-card interface

Serial

A popular method of connecting a mouse to most older PC-compatible computers is through a serial interface. As with other serial devices, the connector on the end of the mouse cable is either a 9-pin or 25-pin male connector. Only a couple of pins in the DB-9 or DB-25 connectors are used for communications between the mouse and the device driver, but the mouse connector typically has all 9 or 25 pins present.

Because most PCs come with two serial ports, a serial mouse can be plugged into either COM1: or COM2:. The device driver, when initializing, searches the ports to determine the one to which the mouse is connected.

Because a serial mouse does not connect to the system directly, it does not use system resources by itself. Instead, the resources used are those used by the serial port to which it is connected. For example, if you have a mouse connected to COM2, it most likely uses IRQ3 and I/O port addresses 2F8h-2FFh.

Motherboard Mouse Port (PS/2)

Most newer computers now come with a dedicated mouse port built into the motherboard. This was started by IBM with the PS/2 systems in 1987, so this interface is often referred to as a PS/2 mouse interface. This term does not imply that such a mouse can work only with a PS/2; instead, it means that the mouse can connect to any system that has a dedicated mouse port on the motherboard.

A motherboard mouse connector usually is exactly the same as the mini-DIN connector used for newer keyboards. In fact, the motherboard mouse port is connected to the 8042-type keyboard controller found on the motherboard. All the PS/2 computers include mini-DIN keyboard and mouse port connectors on the back. Most compatible Slimline computers also have these same connectors for space reasons. Other motherboards have a pin-header type connector for the mouse port because most standard cases do not have a provision for the mini-DIN mouse connector. In that case, an adapter cable is usually supplied with the system that adapts the pin-header connector on the motherboard to the standard mini-DIN type connector used for the motherboard mouse.

Connecting a mouse to the built-in mouse port is the best method of connection because you do not lose any interface slots or any serial ports, and the performance is not limited by the serial port circuitry. The standard resource usage for a motherboard (or PS/2) mouse port is IRQ 12 and I/O port addresses 60h and 64h. Because the motherboard mouse port uses the 8042-type keyboard controller chip, the port addresses are those of this chip. IRQ 12 is an interrupt that is usually free on most systems and, of course, must remain free on any ISA bus systems that have a motherboard mouse port because interrupt sharing is not allowed with the ISA bus.

Serial and Motherboard Mouse Port (PS/2)

A hybrid type of mouse can plug into both a serial port or a motherboard mouse port connection. This combination serial-PS/2 mouse is the most popular type because it is more flexible than the single design types. Circuitry in this mouse automatically detects the type of port to which it is connected and configures the mouse automatically. These mice usually come with a mini-DIN connector on the end of their cable and also include an adapter between the mini-DIN to a 9- or 25-pin serial port connector.

Sometimes people use adapters to try to connect a serial mouse to a motherboard mouse port, or a motherboard mouse to a serial port. This does not work and is not the fault of the adapter. If the mouse does not explicitly state that it is both a serial-PS/2 type mouse, it does not work on either interface but instead works only on the single interface for which it was designed. Most of the time, you find the designation for what type of mouse you have printed on the bottom of it.

Bus

A bus mouse is typically used in systems that do not have a motherboard mouse port or any available serial ports. The name bus mouse is derived from the fact that the mouse requires a special bus interface board that occupies a slot in your computer and communicates with the device driver across the main motherboard bus. Although the use of a bus mouse is transparent to the user (there is no operational difference between a bus mouse and other types of mice), many people view a bus mouse as less desirable than other types because it occupies a slot that could be used for other peripherals.

Another drawback to the bus mouse is that it is electrically incompatible with the other types of mice. Because it is not very popular, a bus mouse can be hard to find in a pinch. Likewise, the bus adapters are typically available only for ISA slots; because they are always 8-bit cards, you are limited in the choice of nonconflicting hardware interrupts. A bus mouse can also be dangerous because it uses a mini-DIN connector just like the motherboard (PS/2)-type mouse, although they are totally incompatible. I have even heard of people damaging motherboards by plugging a bus mouse into a motherboard mouse connector.

Bus mouse adapter cards usually have a selectable interrupt and I/O port address setting, but the IRQ selection is limited to only 8-bit interrupts. This usually means that you must choose IRQ 5 in most systems that already have two serial ports because all the other 8-bit interrupts will be used. If you also are using another 8-bit-only card that needs an interrupt, like some of the sound cards, you will not be able to run both devices in the same system without conflicts. All in all, I do not recommend bus mice and think they should be avoided.

> NOTE: Microsoft sometimes calls a bus mouse an inport mouse, which is its proprietary name for a bus mouse connection.

### Mouse Troubleshooting

If you are experiencing problems with your mouse, you need to look in only two general places--hardware or software. Because mice are basically simple devices, looking at the hardware takes very little time. Detecting and correcting software problems can take a bit longer, however.

Hardware Problems

Two types of hardware problems can crop up when you are using a mouse. The most common is a dirty mouse, which is fixed by doing some "mouse cleaning." The other relates to interrupt conflicts and is more difficult to solve.

Cleaning Your Mouse

If you notice that the mouse pointer moves across the screen in a jerky fashion, it may be time to clean your mouse. This jerkiness is caused when dirt and dust get trapped around the mouse's ball and roller assembly, thereby restricting its free movement.

From a hardware perspective, the mouse is a simple device, and cleaning it is also very simple. The first step is to turn the mouse housing over so that you can see the ball on the bottom. Notice that surrounding the ball is an access panel that you can open. There may even be some instructions that indicate how the panel is to be opened. (Some off-brand mice may require you to remove some screws to get at the roller ball.) Remove the panel, and you can see more of the roller ball and the socket in which it rests.

If you turn the mouse back over, the rubber roller ball should fall into your hand. Take a look at the ball. It may be gray or black, but it should have no visible dirt or other contamination. If it does, wash it in soapy water or a mild solvent such as contact cleaner solution or alcohol and dry it off.

Now take a look at the socket in which the roller ball normally rests. You will see two or three small wheels or bars against which the ball normally rolls. If you see dust or dirt on or around these wheels or bars, you need to clean them. The best way is to use a compressed air duster can to blow out any dust or dirt. You also can use some electrical contact cleaner to clean the rollers. Remember, any remaining dirt or dust impedes the movement of the roller ball and means that the mouse will not work as it should.

Put the mouse back together by inserting the roller ball into the socket and then securely attaching the cover panel. The mouse should look just like it did before you removed the panel except that it will be noticeably cleaner.

Interrupt Conflicts

Interrupts are internal signals used by your computer to indicate when something needs to happen. With a mouse, an interrupt is used whenever the mouse has information to send to the mouse driver. If a conflict occurs and the same interrupt used by the mouse is used by a different device, the mouse will not work properly, if at all.

Interrupt conflicts do not normally occur if your system uses a mouse port, but they can occur with the other types of mouse interfaces. Mouse ports built into modern mother-boards are almost always set to IRQ 12. If your system has a motherboard mouse port, be sure that that you don't set any other adapter cards to IRQ 12 or a conflict will result.

If you are using a serial mouse, interrupt conflicts typically occur if you add a third and fourth serial port. This is because in ISA bus systems, odd-numbered serial ports (1 and 3) are often improperly configured to use the same interrupts as the even-numbered ports (2 and 4). Thus, if your mouse is connected to COM2: and an internal modem uses COM4:, they both may use the same interrupt, and you cannot use them at the same time. You may be able to use the mouse and modem at the same time by moving one of them to a different serial port. For instance, if your mouse uses COM1: and the modem still uses COM4:, you can use them both at once because odd and even ports use different interrupts.

The best way around these interrupt conflicts is to make sure that no two devices use the same interrupt. Serial port adapters are available for adding COM3: and COM4: serial ports that do not share the interrupts used by COM1: and COM2:. These boards enable the new COM ports to use other normally available interrupts, such as IRQs 10, 11, 12, 15, or 5. I never recommend configuring a system with shared interrupts; it is a sure way to run into problems later.

If you suspect an interrupt problem with a bus-type mouse, you can use the Device Manager built into Windows 95 or even a program such as Microsoft's MicroSoft Diagnostics (MSD) to help you identify what interrupt the mouse is set to. You get MSD free with Windows 3.0 or higher as well as MS-DOS 6.0 or higher. If you use OS/2 and/or PC DOS, you can still get MSD for free by downloading it from the Microsoft BBS (see the vendor list).

Beware that programs like MSD that attempt to identify IRQ usage are not always 100 percent accurate--in fact they are inaccurate in many cases--and usually require that the device driver for the particular device be loaded to work at all.

The Device Manager in Windows 95 is part of the Plug and Play (PnP) software for the system, and is usually 100 percent accurate on PnP hardware. Although some of these interrupt-reporting programs can have problems, most will easily identify the mouse IRQ if the mouse driver has been loaded. After the IRQ is identified, you may need to change the IRQ setting of the bus mouse adapter or one or more other devices in your system so that everything works together properly.

If your driver refuses to recognize the mouse at all, regardless of its type, try using a different mouse that you know works. Replacing a defective mouse with a known good one may be the only way to identify if the problem is indeed caused by a bad mouse.

I have had problems in which a bad mouse caused the system to lock just as the driver loaded or even when diagnostics such as MSD attempted to access the mouse. You can easily ferret out this type of problem by loading MSD with the `/I` option, which causes MSD to bypass its initial hardware detection. Then run each of the tests separately, including the mouse test, to see whether the system locks. If the system locks during the mouse test, you have found a problem with either the mouse or the mouse port. Try replacing the mouse to see whether that helps. If does not, you may need to replace the serial port or bus mouse adapter. If a motherboard-based mouse port goes bad, you can replace the entire motherboard--usually expensive--or you can just disable the motherboard mouse port via jumpers or the system setup program and install a serial or bus mouse instead. This enables you to continue using the system without having to replace the motherboard.

Software Problems

Software problems can be a little trickier than hardware problems. Software problems generally manifest themselves as the mouse "just not working." In such instances, you need to check the driver and your software applications before assuming that the mouse itself has gone bad.

Driver Software

To function properly, the mouse requires the installation of a device driver. Under DOS, you have to load the driver manually through your CONFIG.SYS or AUTOEXEC.BAT file, but under Windows the driver is automatically loaded. I normally recommend using the default drivers built into the Windows or OS/2 operating environments, meaning in those environments no additional external driver is necessary. The only reason for loading an external driver (via CONFIG.SYS) is if you want the mouse to work with DOS applications.

If you need the mouse to work under standard DOS--in other words, outside Windows or OS/2--you must load a device driver through either your CONFIG.SYS file or your AUTOEXEC.BAT file. This driver, if loaded in the CONFIG.SYS file, is typically called MOUSE.SYS. The version that loads in the AUTOEXEC.BAT file is called MOUSE.COM. (It is possible that your mouse drivers have different names, depending on who manufactured your mouse.) Again, remember that if you only use a mouse under Windows or OS/2, no external drivers are required because the mouse driver is built in.

The first step is to make sure that the proper command to load the driver is in your CONFIG.SYS or AUTOEXEC.BAT file. If it is not, add the proper line, according to the information supplied with your mouse. For instance, the proper command to load the mouse driver through the CONFIG.SYS file for a Microsoft mouse is as follows:

    DEVICEHIGH=\DOS\MOUSE.SYS

The actual working or syntax of the command may vary, depending on whether you are loading the device into upper memory and where the device driver is located on your disk.

One of the biggest problems with the separate mouse driver is getting it loaded into an Upper Memory Block (UMB). The older drivers--9.0 and earlier--require a very large block of 40K to 56K UMB to load into, and upon loading they shrink down to less than 20K. Even though they only take 20K or less after loading, you still need a very large area to get them "in the door."

The best tip I can give you with respect to these separate drivers is to use the newest 9.01 or higher drivers from Microsoft. This new driver is included with the newer Microsoft mice, and is also sold separately as an upgrade. The Microsoft driver works with any type of Microsoft-compatible mouse, which basically means just about any mouse at all. Microsoft requires that you pay about $50 for an upgrade to the newer versions of the mouse driver. You can also get the new driver with a new mouse for $35 or less, which makes the driver-only purchase not very cost-effective. Microsoft still includes only the older driver with DOS 6.22 or earlier. IBM included the new driver with PC DOS 6.3 but switched back to the 8.2 driver in PC DOS 7.0.

If you use version 9.01 or later, it will require less memory than previous versions and will automatically load itself into high memory as well. One of the best features is that it first loads itself into low memory, shrinks down to about 24K, and then moves into upper memory automatically. Not only that, but the driver seeks out the smallest UMB that can hold it, instead of trying only the largest, as would happen if you use the `DEVICEHIGH`, `LOADHIGH`, or `LH` commands to load the driver. Previous versions of the driver could not fit into an upper memory block unless that block was at least 40K to 56K or larger in size, and would certainly not do it automatically. The enhanced self-loading capability of the mouse driver 9.01 and higher can save much memory space and is very much worth having. I hope that this type of self-loading and self-optimizing technique will be used in other device drivers. It will make memory management much easier than it currently is.

After placing the proper driver load command in your CONFIG.SYS or AUTOEXEC.BAT file, reboot the system with the mouse connected and observe that the driver loads properly. If the proper command is in place and the driver is not loading, watch your video screen as your system boots. At some point, you should see a message from the mouse driver indicating that it is loaded. If instead you see a message indicating that the loading was not done, you must determine why. For example, the driver may not be able to load because not enough memory is available. After you determine why it is not loading, you need to rectify the situation and make sure that the driver loads. Again, the new 9.01 or higher driver versions help greatly with memory problems.

It is also possible that some software requires a certain mouse device driver. If you are using an older mouse driver and your application software requires a newer-version mouse driver, the mouse may not work properly. In such cases, contact your mouse vendor directly and request a mouse driver update. Often you can get these through the vendor's BBS or on CompuServe; however, Microsoft charges for its new drivers and does not make them available on its BBS. In that case, it is cheaper to purchase an entire new mouse, which includes the new driver, rather than just the driver upgrade.

Application Software

If your mouse does not work with a specific piece of application software, check the setup information or configuration section of the program. Make sure that you indicated to the program (if necessary) that you are using a mouse. If it still does not work and the mouse works with other software you are using, contact the technical support department of the application software company.

### Trackpoint II/III

On October 20, 1992, IBM introduced a revolutionary new pointing device called TrackPoint II as an integrated feature of its new ThinkPad 700 and 700C computers. Often referred to as a pointing stick device, it consists primarily of a small rubber cap that appears on the keyboard right above the B key, between the G and H keys. This was the first significant new pointing device since the mouse had been invented nearly 30 years earlier!

This device occupies no space on a desk, does not have to be adjusted for left-handed or right-handed use, has no moving parts to fail or become dirty, and--most important--does not require you to move your hands from the home row to use. This is an absolute boon for anybody who is a good typist.

I was fortunate enough to meet the actual creator and designer of this device in early 1992 at the spring COMDEX/Windows World in Chicago. He was in a small corner of the IBM booth showing off his custom-made keyboards with a small silicone rubber nub in the middle. In fact, the devices he had were hand-built prototypes installed in standard desktop keyboards, and he was there trying to get public reaction and feedback on his invention.

I was invited to play with one of the keyboards, which was connected to a demonstration system. By pressing on the stick with my index finger, I could move the mouse pointer on the screen. The stick itself did not move and as such is not a joystick. Instead it had a silicone rubber cap that was connected to pressure transducers that measured the amount of force my finger was applying and the direction of the force and moved the mouse pointer accordingly. The harder I pressed, the faster the pointer moved. I could move the pointer in any direction smoothly, by slightly changing the direction of push or pull. The silicone rubber gripped my finger even though I had been sweating from dashing about the show. After playing around with it for just a few minutes, the movements became automatic--almost as if I could just "think" about where I wanted the pointer to go.

After reflecting on this for a minute, it really hit me: This had to be the most revolutionary pointing device since the mouse itself! Not only would this be a natural replacement for a mouse, but it would also be a boon for touch typists like me who don't like to take their hands off of the keyboard.

The gentleman at the booth turned out to be Ted Selker, the primary inventor of the device. He and Joseph Rutledge created this integrated pointing device at the IBM T.J. Watson Research Center. When I asked him when such keyboards would become available, he could not answer. At the time, there were apparently no plans for production, and he was only trying to test user reaction to the device.

Just over six months later, IBM announced the Thinkpad 700, which included this revolutionary device, then called the Trackpoint II Integrated Pointing Device. Since the original version came out, an enhanced version with greater control and sensitivity called the Trackpoint III has become available.

> NOTE: The reason the device was called trackpoint II is that IBM had previously been selling a convertible mouse/trackball device called the trackpoint. No relationship exists between the original trackpoint mouse/trackball, which has since been discontinued, and the trackpoint II integrated device. Since the original Trackpoint II came out, an improved version called Trackpoint III is now available. It is basically an improved version of the same thing. In the interest of simplicity, I will refer to all of the Trackpoint II, III, and successive devices as just trackpoint.

In final production form, the trackpoint consisted of a small red silicone rubber knob nestled between the G, H, and B keys on the keyboard. Two buttons are placed below the space bar to emulate the LH and RH mouse buttons for making selections. These buttons also can be easily reached by your thumbs without taking your hand off the keyboard.

IBM studies conducted by Selker found that the act of removing your hand from the keyboard, reaching for a mouse, and replacing the hand on the keyboard takes approximately 1.75 seconds. If you type 60 wpm, that can equal nearly two lost words, plus in that time you can lose your train of thought. Almost all this time can be saved each time the trackpoint is used to either move the pointer or make a selection (click or double-click). The combination of the buttons and the positioning knob also enable drag and drop functions to be performed easily as well.

IBM's research also found that people can get up to 20 percent more work accomplished using the trackpoint instead of a mouse, especially where the application involves a mix of typing and pointing activities such as with word processing, spreadsheets, and other typical office applications. In usability tests with the Trackpoint III, IBM gave a number of them to desktop computer users, along with a mouse. After two weeks, 80 percent of the users had unplugged their mice and switched solely to the trackpoint device. Selker is convinced (as am I) that the trackpoint is the best pointing solution for both laptop and desktop systems as well.

Another feature of the trackpoint is that a mouse can be connected to the system to allow for dual-pointer use. In this case, a single mouse pointer would still be on the screen; however, both the Trackpoint and the simultaneously connected mouse could move the pointer. This allows not only the use of both devices by a single person, but in fact two people can use both the Trackpoint and the mouse simultaneously to move the pointer on the screen. The first pointing device that moves takes precedence and retains control over the mouse pointer on the screen until it completes a movement action. The second pointing device is automatically locked out until the primary device is stationary. This enables both devices to be used, but prevents each one from interfering with the other.

Recognizing the significance of the Trackpoint especially for portable systems, several other manufacturers of laptop and notebook portable computers such as Toshiba and TI have licensed the trackpoint pointing device from IBM. Often they will give it a different name, although the technology and operation is the same. For example Toshiba calls it Accupoint on its systems.

I have compared the trackpoint device to other pointing devices for notebooks, such as the trackballs and even the capacitive touch pads, and nothing compares for accuracy, control, and of course the fact that you don't have to take your hands off of the keyboard!

Unfortunately, many of the lower-end portable system manufacturers have chosen not to license the IBM trackpoint technology, but instead have attempted to copy it using inferior transducers and control software. The major drawback to these non-licensed trackpoint type devices is that they simply do not perform as well as the official versions licensed from IBM. They are usually slow to respond, sluggish in operation, and lack the sensitivity and accuracy found in the IBM designed versions.

One way of telling that the trackpoint device is licensed from IBM and uses the IBM technology is that it will accept IBM Trackpoint II or III rubber caps. These have a square hole in them and will properly lock on to any of the licensed versions such as those found in Toshiba systems.

IBM recently upgraded this system and now calls it Trackpoint III. There are two main differences in the III system over the II, but the one that is directly noticeable is the rubber cap itself. IBM always uses red caps in their Trackpoint device while other companies use different colors (Toshiba uses green or gray), although the color itself is unimportant. In any case, the main difference in the new Trackpoint III caps is in the rubber composition, not the color.

The IBM Trackpoint II and Toshiba Accupoint caps are made out of silicone rubber, which is grippy and works well in most situations. However, if the user has greasy fingers, the textured surface of the rubber can absorb some of the grease and become slippery. Cleaning the cap (and the user's hands) solves the problem, but it can be annoying at times. The new Trackpoint III caps are made out of a different type of rubber, which Selker calls "plastic sandpaper." This type of cap is much more grippy, and does not require cleaning except for cosmetic purposes. I have used both types of caps and can say for certain that the Trackpoint III cap is superior!

> NOTE: Since the Accupoint device used in the Toshiba notebooks is licensed from IBM, it uses the same hardware (a pressure transducer called a strain gauge) and takes the same physical caps as IBM's product. What I did was order a set of the new Trackpoint III caps and install them on my Toshiba portable systems, which dramatically improved the grip. You can get these caps by ordering them from IBM Parts directly or from others who sell IBM parts such as DakTech under IBM part number 84G6536; the cost is approximately $9 for a set of two "plastic sandpaper" red caps.

Replacing the cap is easy--simply grab the existing cap with your fingers and pull straight up; it will pop right off. Then push on the new red IBM Trackpoint III cap in its place. You will thank me when you feel how you can grip the new IBM cap much more easily than compared to the designs used by others.

The other difference between the Trackpoint II and III from IBM is in the control software. IBM added routines that implement a subtle technique Selker calls "negative inertia," but which is marketed under the term QuickStop response. This software not only takes into account how far you push the pointer in any direction, but also how quickly you push or release it. Selker found that this improved software (and the sandpaper cap) allows people to make selections up to 8 percent faster.

The trackpoint is obviously an ideal pointing device for a laptop system where lugging around an external mouse or trackball can be a pain. The trackballs and mini-trackballs built into some laptop keyboards are also very difficult to use and usually require removing your hands from the home row. Mouse and trackball devices are notorious for becoming "sticky" as the ball picks up dirt that affects the internal roller motion. This is especially aggravated with the smaller mini-trackball devices.

Many newer notebook systems include a touch pad, which although it seems like a good idea at first, pales in comparison to the trackpoint. The touch pads work on a capacitive effect, and pointer operation can become erratic if your skin is either too dry or too moist. Their biggest drawback is that they are positioned on the keyboard below the spacebar, which means you either have to remove your hand from the home row to place your index finger on the pad, or try to use the pad with your thumb, which has too wide a contact area for precise movement and control.

The bottom line is that anybody who touch types should strongly consider only notebook systems which include an IBM-licensed trackpoint device (such as Toshiba). trackpointers are far superior to other pointing devices such as the touch pads, because the trackpoint is faster to use (you don't have to take your hands off of the home row on the keyboard), easier to adapt to (especially for speedy touch typists), and far more precise.

But the benefits of the trackpoint are not limited to laptop systems. Because I use a notebook so often and have found the Trackpoint system so fast and easy to use, I also wanted to use it on my desktop systems as well. For desktop systems I use a Lexmark keyboard with the IBM-licensed trackpoint device built-in. This makes for a more consistent interface between desktop and notebook use because I can use the same pointing device in both environments. One drawback for some older systems is that the Track-point device in these keyboards works only with systems that used a PS/2- or motherboard-type mouse connector; no serial version is available. I list the part number for the IBM enhanced keyboard with the trackpoint in the section "Replacement Keyboards" earlier in this chapter. You can also purchase these keyboards directly from Lexmark.

The trackpoint probably stands as the most important and revolutionary new pointing device since the original invention of the mouse. As IBM licenses this technology to other manufacturers, you will see this device show up in many different systems. It is already available built into keyboards, which can upgrade many existing systems, and companies such as Toshiba are using this IBM-developed technology in their own systems.

### Glidepoint

In response to the trackpoint, other companies have adopted new pointing device technology as well. For example, Alps Electric has introduced a touch pad pointing device called the glidepoint. The glidepoint uses a flat square pad, which senses finger position through body capacitance. This is similar to the capacitance-sensitive elevator button controls you sometimes encounter in office buildings or hotels. Instead of sitting in between the keys, the glidepoint is mounted below the space bar, and detects pressure applied by your thumbs or fingers. Transducers under the pad convert finger movement into pointer movement. Several laptop and notebook manufacturers have licensed this technology from Alps and are incorporating it into their portable systems. Apple was one of the first to adopt it in its portable systems.

Although it seems to have gained wide acceptance, this technology has a number of drawbacks. Operation of the device can be erratic depending on skin resistance and moisture content. The biggest drawback is that to operate the touch pad, users have to remove their hands from the home row on the keyboard, which dramatically slows them down. In addition, the operation of the touch pad can be imprecise depending on how pointy your finger or thumb is!

On the other hand, if you're not touch typist, then removing your hands from the keyboard to operate the touch pad may be easier than using a trackpointer. Even with its drawbacks, touch pad type pointing devices are still vastly preferred for portable systems over using a trackball or a cumbersome external mouse.

## Game Adapter (Joystick) Interface

The game control or joystick adapter is a special input device that enables up to four paddles or two joysticks to be attached to a PC system. The term paddle is used to refer to a knob that can be rotated to move an object on the screen, and was named after the first popular videogame called Pong, where the knob moved the game paddles.

The game adapter function can be found on a dedicated ISA or MCA bus adapter card, or can be combined with other functions in a multifunction card. The game connector on the card is a female 15-pin D-Shell type socket (see Figure 9.14).

The game adapter can recognize up to four switches (called buttons) and four resistive inputs. Each paddle normally has one button and one knob that controls a variable resistor, whereas a joystick normally has two buttons and a central stick that controls two variable resistors. In a joystick, the variable resistors are tied to the central stick. One indicates the relative vertical position (or x-coordinate) of the stick, and the other indicates its relative horizontal position (or y-coordinate).

Resistor inputs are variable from 0 to 100K ohms. The adapter converts the resistive value to a digital pulse with a duration proportional to the resistive load. Software can time these pulses to determine the relative resistance value. The game adapter does not use much in the way of system resources. The card does not use an IRQ, DMA channel, or memory and requires only a single I/O address (port) 201h. The adapter is controlled by reading and writing data to and from port 201h.

FIG. 9.14 Typical game adapter and 15-pin connector.

Note that joystick resistance is read by polling the adapter; the game port interface is not interrupt driven. This means that a program has to scan the device by sending an I/O command for input rather than by receiving an interrupt as with other (such as serial) devices.

Table 9.13 shows the interface connector pinout specification for a PC-compatible game adapter.

#### Table 9.13 PC-Compatible Game Adapter Connector

Pin | Signal | Function | I/O
1 | +5v | Paddle 1, Joystick A | Out
2 | Button 4 | Paddle 1 button, Joystick A button #1 | In
3 | Position 0 | Paddle 1 position, Joystick A x-coordinate | In
4 | Ground | -- | --
5 | Ground | -- | --
6 | Position 1 | Paddle 2 position, Joystick A y-coordinate | In
7 | Button 5 | Paddle 2 button, Joystick A button #2 | In
8 | +5v | Paddle 2 | Out
9 | +5v | Paddle 3 and Joystick B | Out
10 | Button 6 | Paddle 3 button, Joystick B button #1 | In
11 | Position 2 | Paddle 3 position, Joystick B x-coordinate | In
12 | Ground | -- | --
13 | Position 3 | Paddle 4 position, Joystick B y-coordinate | In
14 | Button 7 | Paddle 4 button, Joystick B button #2 | In
15 | +5v | Paddle 4 | Out

Because this adapter actually reads resistance and can be easily manipulated with standard programming languages, the game adapter serves as a poor man's data acquisition board or real-time interface card. With it, you can hook up to four sensors and four switches and easily read the data in the PC.

Game adapters are available for ISA and MCA bus systems from a number of vendors. Consult the vendor list for some companies that may offer these types of adapters. Generally, the best place to look is one of the larger mail order system and peripheral vendors.

Some manufacturers have produced specialized joysticks that really don't look like joysticks at all. Perhaps the best known of these are the steering wheel and pedal control sets sold for use with driving and flight simulator games. These are really exactly the same as the standard joystick and paddles as far as your system is concerned. Instead of paddle knobs, they have steering wheels and pedals controlling the variable resistors in the circuit. There are a number of these devices on the market for the popular driving and flight simulator games, and they can make these games much more realistic. Because the different controls can be connected to different paddle inputs on the game adapters, make sure that your software will support the particular control device you select.

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