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Appendix C Keyboard
Compaq Personal Computers
Changed - July 2000
C-4
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.