Help identifying UNIBUS PDP-11 CPU upgrade

Josh Dersch derschjo at
Sat Jul 1 00:10:48 CDT 2017

On 6/30/2017 7:30 AM, Noel Chiappa via cctalk wrote:

>      > From: Josh Dersch
>      >> Now I'm confused. There is no cable from the front panel to the CPU in
>      >> a standard 11/34? (There's one from the front panel to the backplane;
>      >> another from the front panel to the M9301; and another from the
>      >> programmer's front panel [if present] to the programmer's front panel
>      >> board, the M7859
>      > Front panel to the CPU upgrade, not the original CPU. ...
>      > there's a pair of connectors on the CPU board that look suspiciously
>      > like those on the M7859.
> Right, that's what's confusing me. I can't work out what you could possibly
> be cabling to, on the new CPU board!

There's a 20-pin header on the CPU upgrade board which connects to the 
front panel.  There's also a single 10-pin header whose function I can't 

> Those two connectors on the M7859 are used only with the 11/34, not the 11/04
> (the cable from the M7859 to the programmer's front panel must be there, with
> both); they are there for the micro-code single-stepping function on the
> 11/34, etc. (One cable carries uclock, the other uPC data.)
> Since the new CPU probably doesn't have that ability (on the LSI-11 and F-11
> chipsets, the micro-word bus is accessible outside the chips, but AFAIK the
> same is not true of the J-11), I'm not at all sure what those two connectors
> might be.

Yes, the programmer's panel loses most of its functionality (as I'd 
expect, for the reasons you list) but the HALT/SS and BOOT switches are 
functional with the cable connected.   (The ADDRESS/DATA display just 
shows "7" for whatever reason.)  With the 20-pin cable from the front 
panel disconnected, the HALT and BOOT switches are non-functional.

> Perhaps they are serial lines using the 'new' DEC standard pinout, which also
> use 10-pin headers?

That's possible.   If so, the one on the CPU doesn't appear to conflict 
with the M7856 I already have in the /34.

- Josh

> 	Noel

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