RE: C64 Keyboard Scanning

From: COPLIN, Nicholas. (
Date: 2000-10-10 10:14:53

Hi Spiro, 
[COPLIN, Nicholas.]  
> At first, it sets all rows, testing if there is any key pressed. If not,
> that's all. If one was pressed, the kernal tests the  rows one by one to
> identify the key. But it does not use any other combination (2..7 rows at
> once).
[COPLIN, Nicholas.]  So the feedback scheme is possible, but would require
four-bit logic? 

Keyboard scanning:
00000000 or 01111111 or 10111111 or 11011111 etc

Feedback codes:
xxxx0011	start rumbler
xxxx1100	stop rumbler (or power on condition)

btw, do I have it correct in that normally port A does the driving, port B
is read? Is there any *danger* if with interrupts disabled I reverse this
(first making both inputs).



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