[Coco] [Color Computer] CoCo Key Press routine

[Robert Gault]

Alan wrote:
> Hi All,
> 
> Can someone tell me how to read a key from the keyboard on a Coco in 
> 6809 assembly language, without using ROM routines? I know I can call a 
> routine at $ADFB and it will wait for a keypress. How can I do the same 
> exact thing without calling a ROM routine? I know it has something to 
> do with scanning the PIA input lines. Any help would be appreciated!
> 

You want to study page 40 in the Coco3 service manual, which shows the 
keyboard matrix. The value in $FF02 represent the columns and the value 
in $FF00 represents the rows.
Studying the "Unravelled" code at $A1CB will give you an example of how 
the matrix is used to determine keys pressed.