Atari 8-bit 6520 chip

[+Propane13]

Hello,

 

I need some information about the 6520 chip that the atari 8-bit computers use. I did some research, and it looks like the most useful parts for me are the following 4 bytes:

 

PORTA

PORTB

PORTACTL

PORTBCTL

 

Problem is, I don't understand

1) what they do

2) the bit-level breakdown (i.e. if I set bit 6 of PORTACTL, what happens?)

 

Can anyone aid in providing me this information, or a place where I can look?

 

Thanks,

-John K. Harvey

[DanBoris]

Check out the book Mapping the Atari which you can read on-line here:

 

http://www.atariarchives.org/mapping/memorymap.php

 

There is a section on the PIA port and what each address does.

 

Dan