On 4 Mar 2010 at 10:20, Keith wrote:
I've read some passing threads about the percom
data separator.
Sounds pretty neat.
Anyone have schematic, or know the chips involved -- or can tell me
how this thing did its job?
You could almost draw the schematic from this photo:
http://www.oldatheart.co.uk/trsmod1-6.jpeg
It appears to be your basic one-shot data separator (or "seperator"
if you wrote the techref for WD). This appears to be a later
production version, as the original versions had 10-turn trimpots
where the 5% resistors are. Doubtless someone figured at the factory
that the expensive pots could be replaced by fixed resistances at
some point. What's most puzzling is the use of an MC836P DTL hex
inverter. Did all boards have this part?
There were certainly much better data separator circuits at the time--
you need only look at the 1771 app notes. Why Tandy decided to use
the 1771 on-chip separator is a mystery, particularly when WD made no
secret of the fact that it was terrible. Even the onboard SA-800
separator was better.
--Chuck