[Coco] Source code for High Speed Bit-Banger I/O

Darren A. darccml at hotmail.com
Fri Apr 27 14:35:03 EDT 2007

>From: Roger Taylor
>At 11:01 AM 4/27/2007, you wrote:
>>If that's true then I could only say WOW!  I would have to see a working 
>>demo to believe it. My mind cannot conceive of any way to sync with such a 
>>short start-bit while doing other tasks. I hope you will reveal your 
>>secrets someday.
>The minute I release a demo, Robert Gault or 10 other CoCo gurus will 
>reverse engineer it anyway, so the "secret" will be known!  :)
>Before I do something up I'd rather know what trick everyone would like to 
>see happening from BASIC at this speed (57600 bps or 115200 bps).
>As you said, you'll have to see it to believe it, so maybe the real-time 
>connection needs to be seen or even heard.

Roger, I think we need to clarify things further.

The fact that the 6809 can process incoming bits at115.2K baud is a given.  
Maybe I misunderstood your claim, as I took it to mean that the CoCo can be 
busy flashing the cursor (and I assume checking for keystrokes) while being 
able to sync with a 15.5 cycle start-bit that can arrive at any moment.

I can envision a simple protocol where the PC would first request attention 
from the CoCo by issuing a serial BREAK (holding the data line low) for a 
period just long enough for the CoCo to detect it during an IRQ service 
routine. The CoCo would then transmit an ACK back to the PC saying "I'm 
Ready", enter a tight loop to sync with the expected start-bit, and timeout 
if none is received in very short order.  Once the data starts flowing, the 
CoCo would dedicate all its time to the reception task until complete.

This kind of background processing could be accomplished with the 
subroutines I posted. You just need to implement the higher-level protocol 
on top of them.

I guess I need more detailed info to understand exactly what you are 
claiming to have achieved (maybe more than you are willing to reveal at this 


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