ACT apricot - Page 269

KEYBOARD DRIVER
SYSTEMS INTEREST
The software consists of a number of modules, and
includes
the following specific areas:
1. Keyboard Unit to Apricot serial data handler
2. Key make code (down-code) handler
3. Key break code (up-code) handler
4. Keyboard Data Translation Handler
5. Auto-repeat handler
6. Non-make/break code interpreter
7. Queue handlers for data flow to MS-DOS, screen,
and keyboard
1. Keyboard Unit to Apricot - serial data handler
Serial data from the keyboard unit is received into port B
of the Z80 SIO chip, which causes a receive interrupt
routine to be activated.
This routine, in the SIO handler module, filters out valid
codes from
the keyboard and sends these to the main
keyboard handler routine.
The handler routine in turn filters out all codes not
relating to key make or break operations (up or down codes),
and passes
these on the the non-make/break code
interpreter.