VAX 4000-100 QBUS cables

Noel Chiappa jnc at
Tue Nov 29 11:22:40 CST 2016

    > From: Peter Coghlan

    > Can anyone suggest an existing, simple QBUS device that I could study
    > the documentation of to figure out what a basic QBUS device needs to
    > have and to give me some ideas on how to implement one?

Depends. Do you want to be able to do interrupts? Do you want to be able to
do DMA? Each is a significant increment in complexity.

Later DEC QBUS devices may not be the best things to look at, since they tend
to use special DEC QBUS control chips (I'm _not_ talking about bus
transceiver chips here) which are of course no longer available. 

If all you want is master/slave (i.e. the ability to read/write registers),
try this:  

It implements a single 16-bit register. (Changing it to support a single
block of registers would of course be trivial.)

The switches (and associated comparators) in the lower left allow one to set
the bus address it responds to; the 3 latches on the right hold the register
contents; the drivers/buffers below them drive LEDs to display the register
contents. The control logic is about as simple as it can be; one latch, and a
couple of gates.

You should probably read the QBUS description in any QBUS PDP-11 manual
before attempting to understand it, but having done that, it should be pretty
self-explanatory - the signal names should clue you in to what they mean.

    > From: Glen Slick

    > I have an M9405-PA. It has one male and one female 3-row 50-pin
    > D-shell connector.

That's on the metal plate, right? The board itself should have a 2x25
Berg header.


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