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

Christian Kennedy chris at
Thu Apr 28 21:20:09 CDT 2016

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.

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.

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.

Christian Kennedy, Ph.D.
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"Mr. McKittrick, after careful consideration…"

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