Can't figure out CA and CB ports on 6522

From: J.C.Wren <>
Date: Mon Dec 30 07:35:01 2002

        This looks pretty straight forward, from what I can tell.

        To use the ports as inputs, you need to set DDRA and/or DDRB to 0. In the
ACR, you need to decide if you want the IRA and IRB registers to either be
whatever they are when you read them (bits 1 & 0 == 0), or if you want
whatever is on the pins to be latched on a clock edge on CA1 or CB1 (bits 1
& 0 == 1). By my reading, you can setup all pins as inputs, all as outputs,
or any mixture. The inputs attributes as set by the DDR and the IR
registers will apply to all pins that are inputs, and the reset subject to
the output rules.

        The 6522 is at some base address in memory, say $C800, and occupies 16
sequential addresses. That part I'm pretty sure you already know. Here's a
link to some .tif scans from Rockwell. I couldn't find anything better in
my few minutes of searching.


> -----Original Message-----
> From:
> []On
> Behalf Of Sellam Ismail
> Sent: Monday, December 30, 2002 01:46
> To: Classic Computers Mailing List
> Subject: Can't figure out CA and CB ports on 6522
> 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.
> But how do you set them up as such? The documentation is confusing.
> I'll sleep on it and see if either a) I wake up refreshed and
> figure it
> out or b) wake up and find a nice helpful message waiting here ;)
> Sellam Ismail Vintage
> Computer Festival
> --------------------------------------------------------------
> ----------------
> International Man of Intrigue and Danger
> * Old computing resources for business and academia at
> *
Received on Mon Dec 30 2002 - 07:35:01 GMT

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