Can't figure out CA and CB ports on 6522

From: Jeffrey Sharp <>
Date: Mon Dec 30 07:00:01 2002

On Monday, December 30, 2002, Sellam Ismail wrote:
> I'm having a heck of a time figuring out how to use the CA and CB ports on
> the 6522 as inputs. From the documentation I have, it seems the CA port
> can be used for one TTL input, and CB can be used as two.

This is probably incorrect for your situation, and remember, I ain't no
hardware guy yet. I wrote some firmware for an 8051 clone, a Dallas DS80C520
(IIRC). It had some pins that could be used as input or output. When using
them for input, it was necessary to write a 1 to the pins before reading
them. I know, I know, this is a totally different chip, but just maybe your
situation is similar. The reason for the write had something to do with the
way the I/O pins were built, electrically.

Jeffrey Sharp
Received on Mon Dec 30 2002 - 07:00:01 GMT

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