Standard Telephone & Cable made quite a few phones for British Telecom in the 70s/80s that most people will
recognise instantly even though they didn't actually know who made them. Probably like me they thought that BT made all their own
stuff which I later found out was completely wrong but hey. In the early 80s they branched out into computerised telephones with
this lovely looking beast, the Executel 3910.
David Leevers is the man who designed it, and after I'd tracked him down he said "I built
the first prototype Executel as a commodore Pet, second one was an Apple 2 with small teletext screen in place of the clip on top,
came out in 1984, they built 10,000 but only sold 5000, ahead of its time, cost £6,000 in todays money. I doubt whether the tape
transport still works but the telephone side is OK"
I'd *love* to have seen the Apple][ with the clip-on screen! Obviously my curiosity is piqued as to what
happened to the unsold ones.
Fellow collector Tony brought this one to my attention and on seeing the pictures I said
'what the hells is THAT!' and bought it. It's a desk phone, pure and simple, but massively computerised with an AMD8085 processor
and 32K RAM plus a 5" monitor for displaying diary and phonebook entries AND, and it's a big AND, PRESTEL access!
Back in those days PRESTEL was a big deal and was pushed by the likes of Plessey Communications, Philips
and Mullard who built set-top boxes to access this fledgling information superhighway - very pre-internet. It didn't really take
off though because it relied on the phone network and phone calls were expensive meaning it was only used by businesses.
Note this is different to the Teletext service people remember on their TVs. Several banks tried to push Prestel as a means of
online banking and provided terminals like the Tandata TD1400 to let you manage your accounts from the comfort of your
armchair though please ask the phone bill payer before calling :)
The Viewdata processor is the Plessey MR9735-02 which handled the display of stored pages in its own 1K
RAM and directly drives the 5" B&W screen. Tony's unit also has a small board fitted that allowed an external RGB monitor to be
Communications came courtesy of the Philips (now Signetics) SAA5070 "LUCY" chip which could do 1200/75 baud
modem duties to talk to the outside world amongst other things. More microprocessors powered the keyboard and tape transport which
was also made by Philips. In total this machine has 4 processors, not bad for 1984!
Whilst looking around for people who might've had something to do with the Executel I came across two
names, one still active and one that's disappeared. John Staniland Burton used to run Aston Communications; they
seemed to pride themselves on servicing and repairing Executels. These days their website is a single broken page but I'd love to
get in contact with him.
The other name is Sean Newcombe whose bio says not only was he at STC and oversaw the
design of the Executel but also oversaw the design of the ICL One-Per-Desk a couple of years later after STC bought ICL. I'd been
led to believe the two machines were totally separate but...
These days they're mostly to be found in museums, even the National Trust has one in one of their more
contemporary houses in Esher, Surrey.
Unfortunately plastic hides a multitude of storage sins and this one's internals looked like it had been
kept on its back in a pond since some of the components had rotted. What made things worse was the seller I bought it from had
tried to power it up and let out the magic smoke...the keyboard had also been very wet in the past so I was fearful for its condition.
Vertical learning curve time. Over the months I've drawn out the whole computer side of the system board
in an attempt to learn what it does and identify the chips that have lost their markings. Fortunately I could read all the ROMs
before two of them expired and have disassembled maybe 70% of the code. Some of the components are difficult to find any info on,
particularly the MR9735 and SAA5070 which seem to have been largely forgotten. Programming details on both of them are restricted
to a single datasheet but thankfully for the MR9735 it was also used by Tandata in their TD series of teletext adapters so at least
I could test it.
One thing I'm really missing is the memory map because the 8085 can address 64K of memory and in this
machine's case the bottom 32K is ROM (4x 8K EEPROMs) and the upper 32K is RAM (16x 4116 DRAM), but in amongst that you also have
the 1K of page store for the teletext chip, some space also needs to be reserved for the realtime clock on board and there's other
sundries going on too. Also upper RAM in the $FB00 region is used for the stack pointer and scratch space... there are also plenty
of unknowns, like why the PAL that drives the ROMCS line is fed by the upper address lines but only uses 3 of them.
I've been lucky enough to receive much Executel goodness courtesy of Paul, an ex-STC staffer, clicky here
*Update 2 18/07/2019*
By chance I discovered what happened to the unsold 3910 units - they were turned into consoles for the BT SDX 180 PBX system! See here. There's no extra info about this though, and particularly no pictures of one in use so if you have such a thing please let me know.