[Coco] CoCo SDC and DriveWire

Darren A mechacoco at gmail.com
Sat Feb 20 14:20:58 EST 2016

On Sat, Feb 20, 2016 at 10:04 AM, Barry Nelson wrote:

> I have been using my CoCo SDC on my CoCo 3 with DriveWire and it has been
> working well, however, recently I decided to get my CoCo 1 running with
> DriveWire, so I changed the baud rate on my DriveWire server to 38400,
> wrote a HDBDOS rom for the CoCo 1, hooked it up, and it works. The same rom
> even works on my CoCo 3, as long as I keep the server baud rate set to
> 38400, but, not surprisingly, SDC DOS no longer talks to my DriveWire
> server on my CoCo 3. So, here's the question, where and how can I set the
> baud rate that SDC DOS uses to talk to DriveWire? The SDC DOS feature list
> says it supports quote:
> DriveWire disk protocol with auto-speed configuration for CoCo 1, 2 or 3
> Ok, so is there a way to override the auto detect and set the speed
> manually? Maybe with a poke or a patch? I wish I has the source code to SDC
> DOS.

SDC-DOS has two sets of DriveWire I/O routines. One set has the timing for
38400 bps and the other set for either 57600 or 115200 bps depending on the
CPU speed.  You can control which set of routines is active by entering one
of the following POKEs:

POKE &H77, &HF0     -- 57600 / 115200
POKE &H77, &HF4     -- 38400

When running on a CoCo 3, SDC-DOS will also select the 2Mhz clock speed
(115200 bps) while communicating with the DW server. This presents a
problem if you want to use the 38400 bit rate, since the faster clock speed
will actually double it to 76800. You can try the following POKEs to patch
the code so that SDC-DOS (Version 1.2 only) selects the normal clock speed
instead. I haven't tested this patch, so no gaurantees it will work.

POKE &HDD11, 2

- Darren

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