Anybody know what these boards are?
nbreeden
One of my keyboard units has this board, the other doesn't.
-Neil
Mike Y
"nbreeden" <nbre...@comcast.net> wrote in message
news:521f1334-7b4f-42ab...@k1g2000prb.googlegroups.com...
If I remember this correctly, that appears to be what was called the XRX-III
board. It went into the cassette input circuitry and essentially disabled
it for
a short time period after receipt of a data pulse.
This dramatically improved performance when trying to read noisy tapes.
Later versions of the BASIC did the same thing in firmware.
The problem was that the input routine would look for the presence of the
next data pulse immediately upon reception of a pulse, even though there
was not supposed to be one there, and could confuse noise with data.
Putting the XRX-III on a machine with the later BASIC would not harm
things. Except that it could interfere if you had hacked your machine to
speed up the clock and were trying to also speed up your cassette rate,
depending on how you did your speedup mod.
Mike Yetsko
Mike Y
If you remove an XRX-III, I think theres a single cut that you would need to
put
back.
And the 'DIN' connector in the photo. That was for the second generation of
the
buffered EI cable mod. It's a 6-pin DIN cable that went between the main
CPU
and the early EI boards. Originally the buffered EI cable just buffered the
signals
and ran RAS, MUX, and CAS across the main cable to the EI. However that
proved to not solve the reboot/lockup problem on all machines. The later
fix was
to still use the buffered EI cable, but now the three mentioned signals were
taken
from the CPU board through 3 'twisted wire pairs' through the 6-pin DIN
connector to resistor terminations on the EI.
The DIN cable connector in the photo is just another part, not something to
do
with the small XRX-III circuit boards.
Knut Roll-Lund
Yes I agree.
Just wanted to add that normally only one card is used and it goes
without any connectors with some cut and strap directly onto the main
card. I have this modification in one of my machines. I can look up the
details if you like.
It seems somebody have tried using them for something completely different.
Useful only if you have the original model I ROM which opens up with
'MEMORY SIZE?' (not the later ROM(s) which says 'MEM SIZE?').
--
Knut
(delete 'nogarbage.' for email)