Rolm Computers: 1602, 1602A, 1602B, 1666, MSExx (was Data General Nova Star Trek)

Sean Caron scaron at
Fri Apr 29 00:45:52 CDT 2016

On Thu, 28 Apr 2016, Christian Kennedy wrote:

> On 4/28/16 17:45, Sean Caron wrote:
> [big snip]
>> I find the design of the CBX really interesting. IMO, their appearance
>> belies that ROLM was a computer vendor first a a phone equipment maker
>> second. Not in a perjorative sense, just stylistically. Comparing them
>> against boards from WECo/ATT/Lucent/Avaya, Nortel and Harris.
> I was a staff engineer at ROLM MSC between '82 - '86.  By that time by
> any reasonable measure MSC and telecomm were two utterly different
> companies that happened to have common parentage; technology cross-over
> between the divisions was for all practical purposes nonexistent
> (although we did have the occasional employee move between divisions,
> particularly after the IBM debacle) -- but it certainly seems that
> experience building stuff on the MSC side informed *some* of the early
> design decisions on the telcom side.

Very cool, thanks for the perspective. My understanding was that the 
profits on the mil-spec computers side bankrolled the entry into the PBX 
market but I was never clear on how much overlap there was between the two 
divisions. Any awareness if the common control of the CBX is in any way 
architecturally related to the DG Nova?

It seems like it would be advantageous to leverage the experience building 
mil-spec Nova processors on the other side of the business, and looking at 
the hardware, it is clear the CBX is a 16-bit machine. But never been able 
to confirm.

One thing that would be a huge score for postierity and might help to 
answer some of these questions is a copy of the first half of the System 
Service Manual for the CBX. I have Part II which contains a command 
reference and some discussion of peripheral cards, but everything relating 
to system architecture and the design of the common control seems to be in 
Part I. Do you know of anyone who may have preserved this? I've spoken 
with a few old hands who were CBX switchmen in the past but all I've been 
able to get is Part II.

> IIRC the most interesting thing about the CBX was that it could do so
> much with so little hardware (relative to other switches of the time)
> thanks to TDM of the 12-bit bus through the "connection table", which
> was a 384 slot recirculating command buffer that drove the codecs, dial
> tone generators, tone decoders, ring generators and the like.  Basically
> the CPU would schedule the sender and receiver for the bus by dropping
> commands into two parallel queues (one for transmit, one for receive),
> so there was no need for bus request or arbitration logic and yet the
> CPU could be slow, as the sequencer would just advance through the
> buffer every 83usec processing the commands that it found.  It was a
> pretty clever way of substituting DRAM for bus control logic while
> reducing processor requirements.

I had watched a Youtube video which discussed a little bit about the 

However what you write is much more detailed. I believe there is an 
apocryphal story behind that particular part and sampling rate although 
the specifics elude me at the moment ... I understand it caused trouble 
trying to interface the CBX to DS1 circuits.

> MSC was effectively the alpha site for new builds and new hardware, and
> we saw failures that at times left us without reliable phones for a day
> or two.  One of the more interesting was when the switch refused to
> honor extension status changes and instead entertained itself by ringing
> each extension *once* in ascending order, then repeating.

Sometimes my Definity gets confused and does that. Surprises the heck out 
of my partner and me. Good thing it hasn't happened in the middle of the 
night :O



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