PDP-11/05 restoration project - anyone has a M7810 or M781?

tony duell ard at p850ug1.demon.co.uk
Sun Sep 27 15:47:21 CDT 2015

[Second serial port on a PDP11/05]

> Curious: what if the built in one were
> faulty, or if you wanted to use rs-232
> instead of current loop?

IIRC the 11/05S has a way to disable the built-in
console port (fit a wire link on one of the boards?)
the original 11/05 doesn't. There must be a way to do
it by cutting/jumpering but it is a mess....

Therefore, if the built-in port is faulty it is going to be
a lot less work to fix it than to disable it and add a DL11
Heck, the entire 11/05 CPU is only a couple of hundred ICs,
the serial port is going to be a small fraction of those. It is
not going to be hard to figure out.

As for the physical interface, firstly the OP mentioned a 
teletype, which to me suggests current loop anyway. If
you need RS232 then either pick up TTL level signals on 
the CPU board and add level shifters (very easy, but 
makes the machine not original) or make a current loop
to RS232 interface (not exactly difficult either). I think
both are less work than disabling the built-in port.


- John

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