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

[David Ladd]

Allen,

I can confirm that RX line is used to ACK the receipt of the byte that was
sent to the printer.  When trying to transfer listings from the CoCo using
the bitbanger I had to keep hitting a key on the terminal program to get
basic to keep sending data.

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On Thu, Mar 8, 2018 at 3:48 PM, Allen Huffman <alsplace at pobox.com> wrote:

> 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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