HP21MX booster board?

Bob Shannon bshannon at tiac.net
Sun Aug 14 08:55:54 CDT 2005

I've seen several E-series CPU's fitted with a 'Booster Microcode' board.

The board I'm describing here is just about half the size of the CPU board.
Despite its name, it does not hold microcode ROM's.  It does have a series
of 74S181 ALU chips and other logic that expands the data paths and ALU
of the main CPU.

This board appears to have evolved from the FFT processor options that would
plug into I/O slots.  This configuration it often found in HP's vibration 
and vibration analyzer systems, where there were also microcode ROM's
installed to drive this thing.

I've never found documentation to described the booster microcode board
itself, nor the instructions added by the microcode that drives these 
(It does seem that there is more than one set of microcode ROM's installed
with this board).

In an E-series machine, this board and its additional microcode can be 
to return the CPU to a 'stock' configuration.  Terry Newton's 21MX was just
such a customized processor that was re-configured into a 'stock' E series 
with DMS and FFP for HP-IPL/OS development.

On an M-series I suspect things are a little different, as the M-series CPU 
the mircoprogrammable processor port used to drive this thing (at least 
how its cabled up on HP's vibration control systems).  I'm not sure how the
extra bits of the booster board get mapped into the mircoengine of the M 

I also don't know if your board is exactly the same as the one used on the E
series, but I'd guess its not, due to the lack of the MPP port.

In any case, the E-series version of this board is fairly common, I probably
have 4 or 5 extras, as well as a complete CPU with all the cables and ROM's.

----- Original Message ----- 
From: "Jay West" <jwest at classiccmp.org>
To: "General Discussion: On-Topic and Off-Topic Posts" 
<cctalk at classiccmp.org>
Sent: Saturday, August 13, 2005 1:59 PM
Subject: HP21MX booster board?

>I am doing a little basement cleaning and pitching some things. Was tossing 
>an HP frequency analyzer that was in bad shape and decided to pop the cover 
>and grab the cpu board (the cpu board is a 21MX M-series). Also got 64k 
>memory & controller :)
> My question is two fold -first, what's necessary to use this M series 
> board as a regular processor. I see the base instruction set on the bottom 
> plus two additional non-standard microcode cards. I can just remove those, 
> but didn't know if any changes to the M series board were required. 
> Second, there is a board I've never seen before mounted under the 
> mainboard on the opposite end of the microcode. The board is labled 
> "booster board" and is about 1/2 the size of the main cpu board. I would 
> normally think this was just a specific board to the frequency analyzer, 
> but, I think I've heard Bob Shannon talk about this booster board before 
> in more general terms. Should I keep the booster board?
> Jay West

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