CS 2734 Computer Organization II

• Basic Hardware:
  • Scan matrix which gives an X and Y coordinate of a key press.
  • The coordinates are sent to a keyboard chip which looks up a scan code corresponding to the key. (See http://webclass.cqu.edu.au/Units/81120_FOCT_Hardware/Study_Material/Study_Guide/chap4/chapter4.html for the listing for the standard AT keyboard.)
  • The keyboard sends it as an 11 bit SDU (serial data unit) to the keyboard interface:
    • 0: start bit (always 0)
    • 1-8: DB0 to DB7 (data bits of scan code)
    • 9: parity
    • 10: stop bit (always 1)
• The transfer to the keyboard interface is a synchronous transfer
• The keyboard interface generates data on a synchronous interface with pins:
  • 1: Keyboard clock
  • 2: Keyboard data
  • 3: Keyboard reset
  • 4: Signal ground
  • 5: Vcc
• The AT keyboard chip is programmable.
• How are silent keys handled (like SHIFT or CTRL)?
  • Keyboard first generates the "make code" for the SHIFT (e.g. 42).
  • Keyboard interface generates an interrupt.
  • The device driver gets the interrupt, recognizes it is a SHIFT,
  • Requests the next key scan code (e.g. 46 for 'c').
  • Combines the SHIFT and key to get an uppercase 'C'.
  • Keyboards also have a repetition rate which is 10 char/s on the AT keyboard and programmable on later keyboards.
• Keyboard controller on AT and later keyboards has:
  • Input buffer
  • Output buffer
  • Control register
  • Status register