29 Dec
2002
29 Dec
'02
4:45 p.m.
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
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29 Dec
29 Dec
11 p.m.
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
11:35 p.m.
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. http://bbc.nvg.org/doc/datasheets/R6522_r9.zip
--John
-----Original Message-----
From: cctalk-admin(a)classiccmp.org
[mailto:cctalk-admin@classiccmp.org]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
http://www.vintage.org
* Old computing resources for business and academia at
www.VintageTech.com *
30 Dec
30 Dec
1:32 a.m.
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.
http://bbc.nvg.org/doc/datasheets/R6522_r9.zip
There are scanned datasheets for most all the 6522 versions at
http://www.6502.org/datasheets/datasheets.htm
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