Commands from the System
Reset (Hex FF)
The system lowers the
'clock'
line for a minimum of 12.5
milliseconds. The keyboard then begins to clock bits
on
the
,
data'
line. The result
is
a Reset command causing the keyboard
to reset itself, perform a BAT, and return the appropriate
completion code.
Commands to the System
The following table shows the commands that the keyboard may
send to the system, and their hexadecimal values.
Command
Hex
Value
BAT
Completion
Code
AA
BAT
Failure
Code
FC
Key
Detection
Error/Overrun
FF
The commands the keyboard sends to the system are described
below, in alphabetic order.
BAT Completion Code (Hex
AA)
Following satisfactory completion of the BAT, the keyboard
sends hex AA. Any other code indicates a failure
of
the
keyboard.
BAT Failure Code (Hex FC)
If a BAT failure occurs, the keyboard sends this code,
discontinues scanning, and waits for a system response
or
reset.
4-26
lOl/102-Key
Keyboard