Curious ex-BT modems

From: Jules Richardson <julesrichardsonuk_at_yahoo.co.uk>
Date: Thu Dec 25 06:46:31 2003

Merry Christmas to all!

Obligatory pre-feast Christmas posting...

Hopefully there's some UK telecoms people on the list who can tell me
some more about these. I unearthed a pair of BT modems (look to be from
the mid 1980s), badged as Datel 4961x's.

They're in nice finned metal cases (with plastic end caps; Datel unicase
4001X's) - I think I hung onto them intending on using the shells to
house a pair of amplifiers, having never had any luck getting the modems
to work.

I was about to scrap them, and opened them up to strip and useful parts
first. Now I'm curious.

There's a *lot* of silicon inside these things. Most of the larger chips
appear to be custom, badged in a range from MS2006 to MS2011. One of the
40 pin chips carries the marking "BTRL / 403 / 5113". British Telecom
Research Labs maybe? There are three OKI 40 pin chips too, several ROMs,
and no less than 42 DIP switches internally.

There are six fuses inside - they didn't hold back there.

The rear of the case has a 25 pin DTE socket, a telephone pass-through
socket, PSTN socket for connection to the network - and also a
mysterious "PC" socket (same type as used for the phone network
connection). Any idea what that's for? ("Private Circuit" maybe)

The front has push-switches for 4800 baud operation, plus AL, ST, RDL
and DL. I assume ST is self-test, but I don't know what the others are.
There are status LEDs for 4800 operation, DSR, RFS, TD, CD, RD and test.
Those all make sense.

I remember I never got one of these to talk to a remote modem of any
type. I'm wondering if they're supposed to be used in pairs (or talk to
some specific remote equipment that I don't have) and use some sort of
non-standard data compression, or even encryption.

Any ideas anyone? Anybody know of any UK telecoms lists where there may
be people who can help?

cheers

Jules
Received on Thu Dec 25 2003 - 06:46:31 GMT