DEC pdp 11 "R-K ABBR. BOOT P. C. Board"

Brent Hilpert hilpert at
Wed Oct 7 15:58:38 CDT 2015

On 2015-Oct-06, at 9:18 AM, Henk Gooijen wrote:
> -----Oorspronkelijk bericht----- From: william degnan
> Sent: Tuesday, October 06, 2015 2:26 PM
> To: cctech
> Subject: DEC pdp 11 "R-K ABBR. BOOT P. C. Board"
> What is the purpose of this controller?  It came with a PDP 11/05 system:
> Printed on the controller is
> R-K ABBR. BOOT P. C. Board 609395 Rev B
> 802000 Rev
> I searched around, found nothing specific  Is this a bootstrap board for an
> RK drive?
> -- 
> Bill
> =========
> I am clueless too, but if you want to play Sherlock Holmes,
> it should be possible to figure it out.
> 20 ICs, several will be familiar in use in circuitr for the bus.
> I'd first check whether it is intended for UNIBUS (likely) or QBUS.
> Given the IC types you can estimate the circuit complexity.
> If there are lots of simple gates it is just a puzzle.
> The board has good quality machined pins, so after making pictures
> and a drawing the location of each IC, you could pull them and
> trace every pin, visually and with an Ohm meter. Lots of work, not
> difficult, but very time consuming ...
> Good for the dark evenings :-)

IC date codes are 75/6, I guess that's just late enough to be QBUS, but more likely UNIBUS.

Can't discern all the IC types but some speculation based on what can be seen: the labeled IC could be a 256*4 PROM, when a memory read-cycle is initiated the 74221 monostables sequence the reading of 4-bit chunks into the the 74175 latches to make up a 16-bit word for presentation on the bus.
The jumpers at centre-bottom could be the base address.
A 256*4 PROM would give a 64-word bootstrap.

Easy board to reverse-engineer.

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