[Coco] CoCo 2 bitbanger does 57600bps!

[Roger Taylor]

At 07:34 PM 3/23/2006, you wrote:
>Roger,
>Congratulations on your achievement.  Just to clarify, you're
>rounding the clock rate up in your message right?  I take it that you
>really mean .895 MHz and that you didn't alter the CoCo's actual
>clock speed.

No mods at all, Boisy.  When I say "1mhz" I mean .895, or the standard speed.


>When I developed DriveWire, I experimented with 57600 bps on a CoCo
>2.  Receiving worked with inlined, straight run code, but I found it
>to be flakey when tested with different PCs and operating systems.
>At those higher speeds, it appeared that some serial ports had
>slightly different tolerances, and the bit transition timing was hit
>and miss.  As you know, it's all in (1) how consistently in time the
>CoCo samples the bit and (2) where the CoCo starts sampling the bit.

Yes, the timing is so precise that it took me a week to nail it down.  I 
plan to test more under Windows XP on two computers and Red Hat Linux 9, 
but that's all I have.  Right now I've got the sending computer in a loop 
and the CoCo hasn't missed a character.

>Yes, the PIA on the CoCo 3 can be pushed to 115200 bps as the sender,
>but I had a much harder time getting the CoCo 3 to run at 115200 as a
>receiver.  As I recall, the timing was close but not quite enough to
>detect the start bit with consistency, and I must have tried half a
>dozen permutations of instructions to accomplish the feat.  With a
>6309 in native mode it could be achieved, but I wanted a solution
>that would work with the baseline 6809 running at 1.78MHz.
>At any rate, it was a great learning process for me, and out of it
>came a very successful product.  I'm sure you're having fun
>discovering all of this yourself!

Only a true programmer would call this fun... and it is!  :)

As for doing 115.2Kbps on a CoCo 3 or any CoCo (that can switch into 2mhz 
mode) with a 68B21 for that matter, only a test will prove it.  I haven't 
gotten that far, but when I do I'll be sure to post the news.

One thing's for sure... all those messages over the years saying that the 
CoCo can really only do 1200bps over the bitbanger port needs to be 
squashed for good.  Even the 9600bps limitation comments are ridiculous.  :)




Roger Taylor