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Re: Super Serial Card Question?
Jorge Chamorro Bieling wrote:
Michael J. Mahon <mjmahon@aol.com> wrote:
If you drop a $10 into the 6551 speed register, it runs at 115kbps.
Apparently, this is not well known, since someone sells a "turbo"
option daughterboard to achieve this speed, too.
Michael you're being bad...
Cool!
There's a hardware-based "turbo option daughterboard" because it's not
possible to speed up the SSC to 230.4 kbps via software:
I knew that, but I don't think it's really the point (see below).
(it) "...allows up to 230,400 bps on the Super Serial Card and also for
a second card to be installed in the adjacent Slot...
....with a software option to allow the Super Serial Card to be pushed
past it's original limit of 19.2k..."
That's because highest baudrate the 6551 can be setup for, is, in this
case, 1,843,200/16 == 115,200, or XTAL/16.
To make it run @230.4 kbps, you have to either exchange the XTAL or feed
a clock through the 6551's Receive Clock (RxC) input, there's *no way*
to make it via software.
And I still maintain that if people knew they could get 115kbps with an
unmodified board, then there would be a *very* tiny market for those who
just have to go 230kbps.
Most things that you want to do with data take a while to do, so the
marginal benefit of running the serial link at 230kbps instead of
115kbps is quite small--certainly not enough to justify adding some
relatively rare and expensive hardware.
For example, ADT modified to run at 115kbps is already spending much
of its time doing disk I/O, so doubling the serial speed would have
a relatively small impact on the time to transfer a disk.
-michael
Music synthesis for 8-bit Apple II's!
Home page: http://members.aol.com/MJMahon/
"The wastebasket is our most important design
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