27 Nov
2003
27 Nov
'03
1:57 a.m.
Some place in
the pdp-8E/M docs there must be specs for the TTY and
reader control circuits. Take a look at the TTY I/O prints and see
what devices DEC used to drive the relay circuit.
The circuit used in e/m machines appears to be overkill -- it can drive
100ma, and kinda had me worried. I rechecked the circuit used in the 8L,
and it looks set up for about 30ma. I can do that without too much If I can't find a TTY to test with, I'll just
spec the resister value for
30ma and hope it works out :-).
I take that back. Looking more closely, the return for that circuit is
to -15, not ground. That puts it squarely at 100ma in both cases, which is
more than my circuit can do (50ma).
Vince