Input Devices - Upgrading and Repairing PCs - page 752

Keyboards connected to a USB port work in a surprisingly similar fashion to those connected to
conventional DIN or mini-DIN (PS/2) ports after the data reaches the system. Inside the keyboard,
various custom controller chips are used by different keyboard manufacturers to receive and interpret
keyboard data before sending it to the system via the USB port. Some of these chips contain USB hub
logic to enable the keyboard to act as a USB hub. After the keyboard data reaches the USB port on the
system, the USB port routes the data to the 8042-compatible keyboard controller, where the data is
treated as any other keyboard information.
This process works well after a system has booted into Windows. But what about users who need to
use the keyboard when running an older non-USB aware OS or within the BIOS configuration
routine? That problem is solved by ensuring that USB Legacy support is present and enabled in the
BIOS Setup. (See “ Advanced USB Configuration Menu , ” in Chapter 5 , “ BIOS . ”)
Typematic Functions
If a key on the keyboard is held down, it becomes typematic , which means the keyboard repeatedly
sends the keypress code to the motherboard. In the AT-style keyboards, the typematic rate is adjusted
by sending the appropriate commands to the keyboard processor. This is impossible for the earlier
PC/XT keyboard types because the keyboard interface for these types is not bidirectional.
AT-style keyboards have programmable typematic repeat rate and delay parameters. You can adjust
the typematic repeat rate and delay parameters with settings in your system BIOS (although not all
BIOS chips can control all functions) or in your OS. In Windows you can use either the MODE
command or the Keyboard icon in the Control Panel. Using either method, you can set the repeat rate
from about 2cps (characters per second) minimum to 30cps maximum, and the delay from 0.25
seconds minimum to 1 second maximum.
For the fastest keyboard operation, I like to set the repeat rate to the maximum (30cps) and the delay
to the minimum (0.25 seconds), which can be accomplished with the following command:
MODE CON: RATE=31 DELAY=0
Likewise, slowing the repeat rate to the minimum (2cps) and increasing the delay to the maximum (1
second) can be accomplished with the following command:
MODE CON: RATE=0 DELAY=3
Entering MODE CON: with no other parameters shows the current status of the settings. You can also
modify these settings using the Keyboard icon in the Control Panel. The Repeat Delay slider, shown
in Figure 15.7 , controls the duration for which you must press a key before the character begins to
repeat, and the Repeat Rate slider controls how fast the character repeats after the delay has elapsed.