connecting 33 to PDP-8

From: Ethan Dicks <>
Date: Wed Dec 18 03:14:01 2002

--- wrote:
> On Dec 17, 21:40, Charles wrote:
> > I have a PDP-8/I and a Model 33 but there are no connectors at
> > all. The serial interface card (? M709) is there and if I run
> > clipleads to the appropriate pins on its backplane socket with a
> > series resistor to +12v it works, both keyboard and printer.

I don't have the handbook nor the hardware in front of me to say
which one is which, but the console TTY send/receive boards are
the M706 and M707. TTL in/out. The -8/i uses identical hardware
to the -8/L (I have both)... M452(?) clock generator (I have this
plan in the back of my head to build a xtal-controlled baud rate
generator with a COM8116 or the like). The 20mA paddle card for
both is the W076. If you follow the output pins you've been
hooking up to, you'll find where the W076 lives. Alternatively,
there are schematics and board layout documents on sites like and others.

> > What pieces am I missing? The above discussion is beyond my
> > current understanding of DEC interconnect hardware. Should there
> > be a card that plugs into the backplane somewhere, that has a
> > pigtail hanging from it, or what? If so, what part number should I
> > be searching for?

W076. It will have a few resistors, capacitors and a transistor or
two, and several split lugs. If you happen to pick one up with
no cable or one that you don't know what CPU it came from (it's used
in several), I have seen a document somewhere that describes the
minor differences between types of machines the W076 works in (what
voltages are available on pins like B2 and what not).

Mine came with my M-series machines, so I never had to worry about
moving the wires around.
> There possibly should, but I don't know much about the details of an 8/I.
> Are there wires running from those pins to another slot?

Yes. Unlike OMNIBUS machines, the -8/i (and -8/L, -8/S and Straight-8),
the wiring is, to the casual observer, random, not bussed. It has a
pattern and flow to it, but nothing approaching the predictability
of the OMNIBUS (pin A1 to pin A1, all slots; pin A2 to pin A2, all slots,

> An 8/E is Omnibus, and the serial signals don't appear anywhere on the
> backplane, so the only access is via the Berg connector on the (quad
> height) interface



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Received on Wed Dec 18 2002 - 03:14:01 GMT

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