W076/M452 replacement cards

From: vrs <vrs_at_msn.com>
Date: Thu Nov 27 09:57:01 2003

> > 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
trouble.
> 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
Received on Thu Nov 27 2003 - 09:57:01 GMT