Posted By
Gaia
on 2007-03-27
18:00:11
|  Re: Unknown TED machine?
Me likes it too. A couple of inaccuracies that's all. It has been written with passion and it shows.
Anyway, right off the wire here's some news from Mr Herd himself about the mysterious photograph:
"At first I thought it was a C64CR type
thing but this looks like a member of the TED family, probably a C16. It
has the standard joystick ports so its one of the later strange things like
the C16 that magically appeared. The two resistors on the chip mark it as a
TED where the test mode pins were higher impedance than predicted by the
chip designers and a strong electric field would freeze the counters. The
diodes near the keyboard connector also make it a TED, though there is a
chip missing from my last rev of it, this may be a non-production board (in
fact none with the resistors would have made the airwaves). Since there are
only two chips that look like memory, it is probably 16Mb.
...
Clearly a TED, the unnamed 40pin chip is something like
a 7501 cpu which is a processor with a gated r/w line to hold the line valid
through the DRAM cycle. I added U1 myself as the design when I got to CBM
tried to use the 7406 as a level detecting reset circuit.
The design also called for the data lines to go directly out the keyboard
port (hence diodes, Germanium no less, to keep the data lines from shorting
out when you pressed multiple keys) which was also the joystick port. the
problem was the noise the joystick port would pick up would create sparkles
in the picture due to blown data. I added an 8 bit latch (nmos MOS 8529 or
something like that) to isolate the data lines form the keyboard/joystick.
"
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