Appendix C Keyboard

C.2.2 USB-TYPE KEYBOARD TRANSMISSIONS

The USB-type keyboard sends essentially the same information to the system that the PS/2 keyboard does except that the data receives additional NRZI encoding and formatting (prior to leaving the keyboard) to comply with the USB I/F specification (discussed in chapter 5 of this guide).

Packets received at the system’s USB I/F and decoded as originating from the keyboard result in an SMI being generated. An SMI handler routine is invoked that decodes the data and transfers the information to the 8042 keyboard controller where normal (legacy) keyboard processing takes place.

C-4Compaq Personal Computers

Changed - July 2000

Page 179
Image 179
Compaq W4000 manual USB-TYPE Keyboard Transmissions