[Coco] PC-to-CoCo data transfer techniques

[Roger Taylor]

At 01:01 AM 2/13/2006, you wrote:
>You are very limited when using the bit banger port. If you have an RS-232 
>pack, you should use that.

This I know.  :)  But I beg to differ that the serial port can't be pushed 
way beyond it's "limits".  In fact, nobody has really ever set a limit 
because every trick has yet to be tried.

Here's a trick that I remember discussing with (I think) Sockmaster at 
least 10 years ago.  You can handle high-speed receiving by recording your 
IN signals in a buffer.  You oversample as much as you can and avoid a 
sample-and-wait scheme.  A quick algorithm on the sample buffer could yield 
an averaged set of data that reveals the byte received from the sending 
computer.  For instance, for a certain bitrate you might find yourself 
adding together the sum of all bits recorded on intervals of 256 samples or 
so.  For every 256 samples you would expect those samples to represent the 
bit of data received.  Even if noise is on the line, if you add all the 
samples together and the sum is over a threshold of 128 then I would say 
you've got a High bit.  If it's below 128 then you could safely assume a 
Low bit.  Correct me if I'm wrong (and add to this theory if you like) but 
I think this scheme would yield a much more accurate and faster connection 
at the same time.  Never sample-and-wait if you want to handle high-speed 
or HQ serial data, even audio samples.


>My best results for Coco to PC transfer have been under OS-9 using OSTerm, 
>an RS-232 pack, and HyperTerminal on the PC. Transfers over a null modem 
>cable in both directions can be made at 19200 with no limitations on file 
>size. Results are somewhat worse under Disk Basic using Ultimaterm going 
>from the PC to the Coco but just as good from the Coco to the PC.
>
>The null modem cable is made "off the shelf" parts to go from the PC 
>serial port COM1 to the RS-232 connector. No wires need to be jumpered.

I've got some purchased null-modem adaptors, etc., but I plan on making me 
some personal (hacked) null-modem cables since I have so many RS-232 cables 
around here.

Yes, a cable that performs a job like this pays for itself.  An RS-232 Pak 
is not readily available to everybody these days, or in the past.  I've got 
a hacked DC Modem Pak that I do plan to rig a DB-9 connector to as well.



-- 
Roger Taylor