[Coco] [Color Computer] CoCo Key Press routine

[Alan]

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!