[Coco] Making BASIC not wait for printer.

[Arthur Flexser]

I recall learning of this series of pokes from the manual for Microcom, a
very early and little-remembered cartridge-based communications program
from The Micro Works (not to be confused with Microcom Software, a
prominent CoCo vendor that came on the scene much later).  I remember the
program was unusual in using the cartridge FIRQ and also in including the
source in the documentation, probably because they had no worries of its
being transferred to cassette on account of the cartridge FIRQ use.  I
think it was only 1K long, but still way better than the crappy Vidtex
communications program RS was selling.

It was only years later that I figured out exactly what those pokes did.

Art

On Sun, Mar 26, 2017 at 9:47 PM, Allen Huffman <alsplace at pobox.com> wrote:

> > On Mar 26, 2017, at 5:12 PM, Arthur Flexser <flexser at fiu.edu> wrote:
> >
> > To elaborate, now that the memory of this somewhat comes back to me:
> >
> > The first poke, to $FF23, causes $FF22 to become the data direction
> > register, temporarily replacing $FF22's normal operation.  The second
> poke,
> > to what has become the data direction register, sets the bits of $FF22 to
> > the pattern of inputs and outputs that is desired.  Then the third poke,
> to
> > $FF23, turns off the data direction register, restoring the bits of $FF22
> > to normal operation.
> >
> > There should be a fourth poke, setting $FF22 to zero so that the new
> output
> > bit contains the correct value to tell Basic's printer routine that the
> > serial port isn't busy; at least there was in the version I used years
> > ago.  Probably this final poke can be safely omitted, at least under
> DECB,
> > since it would be unlikely that the serial port would register as busy at
> > the time the data direction register was activated.
>
> Thanks, Art. That’s exactly the type of demystification I was looking for.
>
> I recall finding this POKE (probably in Rainbow) and using it for some
> early modem programs I wrote. I had to dig one of them up tonight to see
> how it worked. I had assumed it was some POKE to a BASIC hook somewhere,
> and when I found them I wasn’t sure how it worked to fool BASIC. Now I get
> it.
>
> I was attempting to send bytes to my Arduino device via OS-9 (since it’s
> all built in, and I can use the “display” command) but that wasn’t working,
> so I went back to BASIC… which also didn’t worked.
>
> I guess I have a fried TTL-to-RS232 adapter. This is why I am a software
> guy.
>
>                 — A
>
>
>
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