Help identifying UNIBUS PDP-11 CPU upgrade

Jerry Weiss jsw at
Wed Jun 28 16:59:19 CDT 2017

> On Jun 28, 2017, at 2:35 PM, Josh Dersch via cctalk <cctalk at> wrote:
> On Wed, Jun 28, 2017 at 11:02 AM, Noel Chiappa via cctalk <
> cctalk at> wrote:
>>> From: Josh Dersch
>>> I pulled the ... bootstrap boards from slot 3 ... The BOOT button
>>> causes the RUN light to momentarily flash, but that's about it.
>> That's not too surprising. The way booting works with the M9301 boot card
>> (not
>> sure if you know this already; if you do, apologies, and ignore) is that
>> the
>> 'BOOT' button simulates a power-fail/restart - i.e. it toggles the 'power
>> OK'
>> line (forget whether it's ACOK or DCOK). When the CPU 'powers up', and
>> tries
>> to fetch the power fail restart vector from 024/6, the M9301 steps on the
>> bus
>> address lines and modified the address to 773024/6, which is in the ROM on
>> the
>> M9301. The new PS/PC retrieved at that point then sends the CPU into the
>> ROM.
>> So, with no M9301 plugged in, it's not too surprising it doesn't do much.
> Yeah, I'm aware (or at least was somewhat aware at one point...) of how
> this works.  I'm just surprised the CPU upgrade board doesn't do something
> similar to provide bootstraps, etc.
> (Or maybe it can -- there are a lot of jumpers and dip switches…)

You certainly have a nice find and congrats on getting it functional.  Is that an FPJ11 chip on the board as well?
It would be interesting to boot RT11 and see what the SHOW CONFIG says.   

I never came across this product in my travels.  A quick look at addresses north of 17773000 as you flip
the dip switches or jumpers should reveal all.  Just don’t forget were you parked..


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