[Coco] Serial I/O / Printer port - “printer ready”, etc.

[Joe Grubbs]

This reminds me of a project my dad and I embarked on when I was like 9 or 10. We had an enormous Data South DS-180 printer with serial and parallel connections. I wanted to be able to print, so we built a cable with the 4 pin DIN and DB25 connectors, tying pin 20 (DTR) from the printer to pin 2 on my Coco. Worked like a champ! I suffered through 600 baud printing at first until I found the POKEs for a bit more speed.


________________________________
From: Coco <coco-bounces at maltedmedia.com> on behalf of Allen Huffman <alsplace at pobox.com>
Sent: Thursday, March 8, 2018 4:48 PM
To: CoCoList for Color Computer Enthusiasts
Subject: [Coco] Serial I/O / Printer port - “printer ready”, etc.

The Serial I/O (printer) port on the CoCo provides transmit (TX), receive (RX), carrier detect (CD) and ground (GND).

I was aware of BASIC hanging if you tried to print and the printer was not online. I had been assuming this was due to using the CD line to indicate the printer was ready, but according to this 1983 Compute! article, it was the RX line:

https://www.atarimagazines.com/compute/issue37/coco_printer.php

This is good, because I was wondering if I could use RX with my SirSound Jr. project instead of the CD line so folks could build one using a $4 Arduino clone and a .92 cent RS232-to-TTL adapter that did not provide CD.

>From an old modem program I wrote, I see this detects carrier:

CD=PEEK(&HFF20)
IF (PEEK(&HFF21) AND 128)=128 THEN carrier detect

And from the 500 POKES, PEEKS and EXECS book in the archive, it shows this for printer ready:

IF (PEEK(&HFF21) AND 1)=0 THEN printer is ready

I don’t have a way to test the printer one, so I ask if someone here could verify this information is correct. I used the CD detect one, so I think it is okay.

Being able to use two sources will enable me to have one indicate “sound playing” and the other to indicate “room in the buffer, you can send more data.”

Fun stuff.

                — A


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