20mA cable details

From: Ethan Dicks <erd_6502_at_yahoo.com>
Date: Mon Dec 16 23:04:01 2002

--- pete_at_dunnington.u-net.com wrote:
> The time has come to hook my ASR33 to the PDP-8/E.

Cool! Good on ya.

> The -8/E has an M8650 (KL8E) which I've been using with RS232. However,
> I have 40-way Berg connectors, and the proper AMP flat 8-way Mate-N-Lok
> connector shells for the 20mA loop, and the male and female pins...

Sounds like you have the basics covered. Don't forget the short jumper
wire at the Berg end that directs the TTL output of the KL8E shift
register to the 20mA output circuit. It's a different loop than the
one you should have right now on your EIA cable.

I've successfully converted COMBOARD cables (synchronous serial to
DB-25 for sync modems or modem elimnators) to PDP-8 EIA cables by
cutting a few wires out, rearranging the remainder, and adding the
output driver selection loop. I haven't yet made any PDP-8 20mA
cables from a COMBOARD cable, but only because I lack a supply of
the Mate-N-Lok housings and uncrimped pins.

> There's a grey 6-core connected to the ASR33, and I *think* the male
> connector (the one with the flat tongue and 6 male pins) goes on this
> cable.


> Therefore the connector with the grooves, which the tongue slides
> into, and the female "pins", does on the cable from to the PDP-8/E's Berg
> connector. Yes?

> Next question is, roughly how long would the original 20mA cable on the
> TTY have been? My memory, reaching back two or more decades, says the
> cable on the KL8E should be about a couple of feet, and the rest is all
> one piece, attached to the TTY.

The TTY cable for the -8/a is spec'ed at one foot long with a female
connector ("1976-1977 small computer handbook", under the entry for
DKC8AA). My ASR-33 cable is about 4 meters with a male connector that
I plug into a short female cable that comes from a W076 board in my -8/L.

> Or would there be a third in between?

I have seen that arrangement on later 20mA equipment (VT220s and DZ-11s)
the equipment had the female connectors and were interconnected with Male-
to-Male 20mA cables. In the days of the ASR-33 and VT52, though, the
terminals had multi-meter male cables that plugged into short female
cables at the CPU.


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Received on Mon Dec 16 2002 - 23:04:01 GMT

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