"Programmer Electronic Control"

PartNo. 51-019-02, NSN 1680-99-652-3410,
Supplier K0656, Marconi Avionics, UK

Alternate designation (unsure!) NSN 5865-99-977-8365, Part No. 51-048-02

(Restoration of a vintage rugged computer from the Tornado aircraft)

With reference to and the historic context of
the Elliott 900 series in general
and the 12/12 and 920ME in particular.

- The complete Story in pictures, by Erik Baigar, www.baigar.de -



10.6.2017: Fixed typos, complete update of the logbook 2015-2017 and Elliott stuff included here directly.
5.6.2017: Major update with revised wanted items, the story on the newly acquired 920ME and addition
of new chapters regarding the historic context and the evolution of the architecture.
28.2.2016: Updated "Wanted Items" (XLS, V1.5), added pictures of paper tape cassettes.
15.7.2015: Additional information (Index, references and part. nos.) to the RPMD-
and FIN demo video on YouTube - HighRes version in preparation.


  1. Results of the reverse engineering efforts
  2. Logbook listing the major steps
  3. Roots of the unit / architecture
  4. Suspected original use
  5. Other applications of the Elliott900 series
  6. Elliott, GEC, Marconi: Historic Context
  7. A mil-spec "full size" 18 bit 920, the 920ME
  8. Simulation for 12bit and 18bit Elliotts
  9. External information
  10. Items Wanted
  12. Picture "gallery"
  13. Older history

1. Result of the reverse engineering efforts from 2004 until today:

Command reference of the "Programmer Electronic Control"

as I deciphered and named the commands. This contains lots of technical information,
timings, pin-outs and much more. Current status: The 12-bit processor is fully
operational - even interrupts and the IO system are working now. A "hello world"
is perfectly running on an attached LCD display and the unit can control a
CalComp M84 pen plotter.

Photo Suite of all the printed circuit boards of the unit:

(1) Driver Board, 1680-99-646-6754; (2) Data Board, 1680-99-646-6755; (3) Core Memory, 5841-99-652-3386;
(4) Driver Board, 1680-99-646-6754; (5) Control Board, 1680-99-646-6753; (6) Data Register, 229-013909;
(7) Data Register, 229-013909; (8) Control Register, 229-013551; (9) Function Decode, 229-013549;
(10) Processor Timing, 229-013547; (11) RxTx Interface, 229-013545; (12) Serial Parallel Converter, 229-016304;
(13) Decode and Interrupt, 229-013905.

The unit consists of 15 boards of standard size 100mm*160mm, containing a total of 497,
mainly standard mil-spec TTL chips. All of them are identified, even the exotic four
custom ones and data-sheets are available. Here is a

Collection of technical information

on all chips used in the PEC's processor including statistics of the date codes.

The next milestones in my hobby is to finish the blinkenlights for the Programmer Electronic Control:
Paper tape, teletype simulation, word generator and register display are working and SAP already runs
nicely. Missing is control of single stepping, run/stop and memory access via the PEC-OMP
(PEC-Operators Monitor Panel).

Current (5/2017) view of the setup: All components including Sun Sparc 20, PEC, logic
analyzer and the homebrew OMP are installed on a movable cart to ease storage:


: Old setup (4/2014) with original panel from Tornado connected for the first time.

2. The Chronology of the project...

...starting in 2004 is a longer story. Thus the complete diary is located on a separate page, listing all major steps
and achievements during the years of reverse engineering: TimeLine. This page contains and explains
many of the pictures shown in the gallery below. The latest achievements from this logbook are the following:




4/9/2014 My automated eBay search sent me an alarm as suspicious PCBs showed up. They looked very similar to the ones I know from PEC, although they are not completely identical. I bid on some of them and contacted the seller: He actually sold me the complete box for a reasonable price and this is how I got hands on 6605-99-525-8290, "DIGITAL COMPUTER UNIT" containing the following 12 PCBs: 6605-99-529-2339, 6605-99-529-2338, 6605-99-529-2323, 6605-99-529-2323, 6605-99-529-2324, 6605-99-529-2337, 6605-99-529-2336, 6605-99-529-2336, 6605-99-529-2335, 6605-99-529-2322, 6605-99-529-2334, 6605-99-529-9118. Unlike PEC the DCU uses software stored in ROM and has semiconductor RAM. Therefor this unit is not freely programmable.

From an expert I got the information that the box was used on the NCS1 gyro compass system. It is indeed an other variant of the 12/12 processor and by 2014 some are still in use.

Two great finds (1) a different 12/12 and (2) the 12 bit Elliott 900 series is still alive around 54 years after the first 900 machine was built!

[NCS1-DCU-3.JPG] [NCS1-DCU-PCBs.jpg]
12/12 (NCS):    12/12 (PEC):
[NCS1-Unit-TimingPCB.jpg] [TornadoUnit-Timing.jpg]
5/3-4/2014 Participation in the Vintage Comuter Festival Europe (VCFe 15.0) in Munich with poster and a talk.
As preparation the homebrew tiny operating system for PEC got some updates and the code was cleaned up. An up-time clock with improved timer handling is added (the timer hardware within PEC really is a bitch) and the AECM panel can be used to start the user processes (currently just one using the plotter to plot a demo graphics). Version of the trivial operating system now is 1.11!
But most important, all equipment survived the transfer to the festival and the two days of demonstration: PEC (Serial 129), Rolm 1602 (Serial 235) and Rolm MSE/14 (Serial 130). The exhibition was awarded the third price by the visitor's election at the end of the festival.
pec-tos V1.11

[AECM-Connected.jpg] [AECM-Connected2.jpg]
[AECM-LampTest.jpg] [AECM-Panel-in-Action-20140309.jpg]
[TornadoCockpit-AECM-Marked.png] [VCFe15.0-CoreOnRolmModule.jpg]
[VCFe15.0-Exhibition.jpg] [VCFe15.0-Explaining.jpg]
[VCFe15.0-PEC1.jpg] [VCFe15.0-PEC2.jpg]
[VCFe15.0-PEC-TOS-Demo.jpg] [VCFe15.0-Talk.jpg]
[VCFe-Exhibition1.jpg] [VCFe-Exhibition2.jpg]




Third vintage computer/avionics biased visit to the UK with (in chronological order):
  • Tech talk with Peter in Milton Keynes including sightseeing in Linford Manor Park and a visit to the local pub.
  • Excursion to the RAF in Marham - the "Home of the Tornados": Really outstanding experience as I have never been within such a facility and that close to fast jets. Terry and I had a "walk around" and "climb onto" with many explanations by our very kind guide!
  • Visit of the "Centre for Computing History", Cambridge - Home of one of the six currently operational 18 bit 900 series Elliott machines restored by Terry.
  • Inspection of the analog mechanical guidance computer on board the HMS Belfast open to the public on river Thames.
  • Meeting with Terry and Valerie in Fleet including a walk in Calthorpe Park and a visit to Blackbushe airport.
  • Sightseeing together with Terry, Valery and Michael in Oxford (including various Colleges with lovely gardens and astonishing buildings).
Many thanks to all who made the stay an exceptional, unforgettable time: Michael, Peter, Rob, Sue, Terry and Valerie!
[CambridgeWithTerry2015.JPG] [HMS-Belfast-ElliottMechComuter2015.JPG]

[HMS-Belfast-GyroCompass2015.JPG] [LondonBigBen2015.jpg]

[OxfordBigHall-2015.JPG] [OxfordLevelyLandscape2015.JPG]


9/16/2016 I just received a new acquisition from eBay: The auction claimed, that the unit is a computer from the Jaguar aircraft named 920ME, part number 75D28482, serial 140 and it should be in serviceable condition. As I was in search for the big 18 bit brother of my Programmer Electronic control (PEC) for many years now, I could not resist to buy it.

A fist inspection shows, that the unit is complete with power supplies and 16k words of memory. The implementation is centered around the AMD minicomputer chips of the AM29xx series and store is implemented using CMOS rams which are buffered by a battery. Checking the memory organization there is even a parity implemented in this unit.

Probably this unit had been sitting in store since 1988, i.e. for 28 years now and I am keen on firing it up again and to complete my collection of the Elliott 900 series!

[920ME-eBay2.gif] [920ME-eBay1.jpg]

[920ME-ConditioningLabel.jpg] [920ME-Memory8k.JPG]

[920ME-16kStore-CompleteMachine.jpg] [920ME-BlackBox.JPG]

3/13/2017 First analysis of the 920ME showed, that the ME's supplies both deliver 5V to two different nets on the backplane. One of the supplies did not work and I had to fix it - herein I noticed, that it contains a manual patch, changing its output from 3.3V to 5V - so probably the chassis of the ME is adapted from an other application where a processor with 3.3V CPU voltage was used.

After some reverse engineering I had identified data- and address busses to the RAM as well as the control signals; I connected a logic analyzer to these signals, showing that after power up there is indeed activity and that the machine starts at 8177 (octal) as is expected from a 18 bit 900 series machine starting without initial instructions (II) engaged.

Of the three front plugs, only SKH has got an easily removable cap which can be "parked" next to the plug. So my assumption was, that this must be the plug for a loading unit and hopefully the machine provides a paper tape interface there. Again after some reverse engineering I identified 8 digital input lines, 8 digital output lines and a hand full of handshake signals. Experiments showed, that one of the signals forces the microcode of the unit to write II to store right after power up and to launch them at 8181. Via two other signals one can send data byte per byte to the initial instructions. After initial excitement I noticed, that after three words got written to store the machine runs havoc.

Investigation showed, that during execution of the II, the instructions are not read from store (although having been written there during startup), but access to the II is trapped by microcode. After the first three words have been written to store, the II transfer control to the newly written words at 8177 and this failed as reading from store did not work correctly (For an explanation of the II in the 900 series, see PAGE7). After a longer search I discovered defective 54138 chips in the memory controller. Later I found an additional such chip in an other subsystem causing problems there and as all had the same date-code I assume that there was a problem unique to exactly this series of the part. Anyhow, after fixing this, loading software worked well for some small self made examples ran nicely! I discovered, that SKH also serves for paper tape punch and teletype in/output via the additional handshake signals.

In the weeks following and in preparation for the CCSs visit, I built an interface emulating a paper tape station and teletype via the 920ME's SKH plug offering hard coded paper tapes one can select from, an USB interface with parity/telecode conversion for teletype and an additional RS232C port for a real paper tape device. This makes my 920ME an complete 900 series 18 bit computer now!

[920ME-BateryReplacement.JPG] [920ME-Debugging.JPG]

[920ME-Interface-20170316.gif] [920ME-LoadingConnector.JPG]

[920ME-LogocAnalyzer-Interface.JPG] [920ME-Repair0.jpg]

6/4/2017 - 8/4/2017 A delegation of the Computer Conservation Society (CCS) visited Munich after they met Horst Zuse in Berlin. I had the opportunity to join them for dinner on Friday and in a guided special tour in the Deutsches Museum. It was great to get in touch with many highly skilled computer experts - the achievements of the CCS in preservation, spreading and reconstruction of vintage computers in the UK are indeed outstanding!
On Sunday Terry (also CCS member) visited me in Aubing, where we played with PEC and after a demonstration of the FIN1010 inertial navigator we focused on working on the 920ME:

Terry had prepared some clever tests to find out whether the 920ME has additional commands implemented (i.e. 905 command set), how the Q register is treated, whether the memory is OK, what side effects there are in instruction 14 (shift) and he also had some nice demos with him. During the tests we had to discover, that there still is a memory problem if there are plenty off accesses to store. So the memory test failed and e.g. the solver for the count down game being a popular television series in the UK fails giving wrong answers! In summary, the 920ME does not have got the 920 ATC command set implemented and it does not have the floating point or stack extensions within its microcode. But it obeys all 920M commands correctly making it a direct replacement!

So the session was a full success, leaving me with some homework to do and lot of new software to explore. Looking forward to get the original 900 series BASIC Terry wrote in the late 1960ties running on the ME...

[CCS-DtMuseum1.JPG] [CCS-DtMuseum2.JPG]

[Setup920ME-X3tests.jpg] [TerryErik-WorkOn920ME.JPG]

5/22/2017 In hunting the memory problem of the 920ME computer I discovered, that it needs an additional supply voltage to drive the memory subsystem (during all experiments until now, this supply was just 1.5V instead of 5.0V simply supplied from the protection diodes within the address driver chips of the memory subsystem).

Although in my opinion it is a design flaw, that the machine starts without this voltage being present, I am happy that it is now working perfectly: Several hours of memory test do not show any issues any more and the software I got from Terry works simply great: BASIC, a solver of the count-down game and CORAL programs compiled externally run if loaded via my paper-tape/TTY simulator interface.

So the 920ME is a machine being compatible to the 920M (with some additional not yet clear functionality) running at the speed of the later 2us-store version of the 920M from the later 1960ties. Although using rather new components (e.g. 2901 as DG Eclipse) the "ME" machine is one of my slowest computers as microcode reduces speed to be compatible with the original 920M.

Probably this machine was designed as a replacement for the Jaguar's NAVWASS system to eliminate the need to support the aging DTL technology of the 920M any longer.

Many thanks to Terry Froggatt for his steady and highly appreciated support with this project - it was and always still is great to learn from him! Thanks also to Allen Vernon from the Bentwaters Cold War Museum where he works on the restoration of Jaguar XX741.

[920ME-AUXsupplyPatch.jpg] [920ME-InterfaceFinal.jpg]

[920ME-RunningBASIC-SavageBenchmark.jpg] [Elliott900implementations.gif]


3. What are the roots of the unit / architecture...

Talking to experts involved with the computer company Elliott (later GEC-Marconi, Marconi Avionics
and today Selex SAS), based in the UK, it was possible to identify the box by comparison of the command set:

The "Programmer Electronic Control" similar to the 12/12 from Elliott.

This is a downsized 12-bit variant of the bigger 18-bit machines of the Elliott 900
series, delivered beginning in 1965. For information on these (e.g. the 920), look at the
"Our Computer Heritage" project of the Computer Conservation Society documenting
British computers.

The following documents have been carefully preserved for over 30 years by
Terry Froggatt and I am really happy that he shared them with me:


The 12-12 essentially is a repacked version of the deskside Elliott 902,
which was optimized for size, power consumption and the other needs of
airborne computing. Following are a picture and the detailed command
description of the "full size" Elliott 902:

902 Facts Card

The following pictures show the early (6/2008) setup of the Programmer
Electronic Control on my bench with and without explanations. In the last
picture you can see an original paper tape (dated 1/10/1970) sitting on
a PCB of the PEC. I got this from Terry Froggatt, too and it contains the ORIGINAL
assembler for the Elliott 902 called SAP or "Symbolic Assembler Program".

with explanations with explanations IRQ bridged

On 5/3/2014 on the VCFe 15.0 in Munich I introduced the Elliott-900 series in a 45min talk to
the audience and an exhibition compared the US made Rolm MIL-SPEC series based on the
Data General architecture to the Elliott 900 (Sorry, German language only!).

Poster -       VCFe 15.0       - Slides

4. Suspected original use of the unit...

Avionics specialists suspect that the Programmer Electronic Control was part of the
first models of Tornado ADV's Foxhunter AI24 radar set. According to the timeline, the PEC
might have been used in Stage1 and before and thus probably was retired in 1991.

There must have been "core store loaders" for in field programming of the units
and "operator data panels" (blinkenlights) for service. But my fear is, that documentation
and all other artefacts are long gone...

Any information, hardware, hints, pictures and discussion is absolutely welcome,
please contact me at erik@baigar.de.

5. Other applications of the Elliott900s...

The PEC's cousin, the Elliott 12-12 computer, was used in various applications starting in the
1970ties and some may still be online today! One example of it's use is the auto-throttle computer
of the Boeing 747-100:

[pics/12-12.jpg] [pics/Minim-Autothrottle.jpg]

The AFDS, the Auotopilot and Flight Director System, forms a vital part of the Tornado's avionics.
These two redundant computers (Part.Nos. 49-134-01 and 49-133-01) control automatic flight of the aircraft
at very low altitudes since its first flight in 1974 using input from the inertial navigator and other sources. The
two redundant computers are EPROM programmed 12 bit machines based on the Elliott 900 architecture are using
CMOS RAM with parity and probably will remain in service until the last Tornado will have gone out of service -
which will be as late as 2020:


Last but not least, the architecture was used for non airborne applications, e.g. the DCU (NSN 6605-99-529-3906,
Part.No. CD 11660) was used in a gyro compass system called NCS1 which was installed on many ships...


In this application, the 12 bit Minim unit has a program in small ROMs together with calibration constants
for compensating the gyroscope's errors in the system. So the architecture is in use for over 50 years
now and surely there are still many more applications I do not know of .... any hints are welcome!

6. Historic context of the Elliott machines (12 and 18 bit)

The following diagram shows a timeline of computing with focus on MIL-SPEC computers
of Elliotts and the rivaling company Rolm (later Loral) from the US. For reference, some
other well known, now vintage, computers and events are listed. The machines from Digital
Equipment are widely known in the "community" whereas the Data General machines form the civil
counterpart to the military Rolm machines (the early variants ip to the Eclipse are binary compatible):

It can be seen, that Elliott has been in the business of computers for a very long time before the other companies
even started their activities where they accumulated lot of experience with analog mechanical computers,
differential analyzers, analog computers and early digital computing - they where among the pioneers of computing!
So they made already computers from 0st to 3rd generation before microprocessors entered the field.
The architecture of the Elliott 900 machines spans the era from 2nd generation computers (1960, i.e. use
of single transistors and magnetic memory) in the early implementations e.g. of the early 903 up to 3rd gen.
computers (i.e. LSI circuits; thanks to Terry Froggatt for permission to use the 903 pictures):

[pics/903-PCB.jpg] [pics/903.gif]

The latest machine of the series I know of, is my 920ME acquired in 2016 via eBay, which implements the architecture
using LSI chips centered around the AM29xx series of the late 1980ties and thus is clearly a 3rd generation implementation
of the architecture (see also next chapter):

[pics/920ME-PCB.jpg] [920ME-16kStore-CompleteMachine.jpg]

Throughout the over 20 years of the evolution of the 900 series, it is highly interesting to note size reduction in the
transition from transistor based implementations occupying several fridge sized cabinets like the 905 to the miniaturized
versions like the 920M using the first chips in DTL technology (TTL or CMOS have not been invented by than). The story continues
to the "ME" above or the even smaller PEC using tiny MIL-SPEC SMD packages:

18 bit, Transistors 905: [pics/905.gif]; 12 bit, 902: [pics/902.gif] and PEC using DIL/SMD: [pics/PEC-PCB.jpg] [pics/PEC.png].

Summarizing the various implementations of the 900 series architecture and their specifications leads
to the following chart where clickable pictures of the machines are repeated below the chart for reference:

[pics/903.gif] [pics/902.gif] [pics/905.gif] [pics/PEC.png] [920ME-BlackBox.JPG]

The machines of the 1960ties are all based on ferrite core memory where the later ones use
CMOS RAM for storing program and data.

It is interesting to note, that the ME despite being some 15 years "younger" than the 920M, runs at the
same speed. The implementation is artificially slowed down by the microcode: Instead of the 150ns cycle
time easily possible with the hardware given, it runs at 10 to 20 micro seconds and thus is one of my
slowest computers. Probably this was done to make it a direct replacement for the 920M used in the
NAVWASS system of the SEPECAT Jaguar aircraft as the 920M's technology was not
repairable any more in the 1980ties.

Last but not least I doubt, there is any other architecture out there, having that log history and having been part
of the computer development from transistors down the road to LSI chips....anyone wants to contradict?

7. A mil-spec "full size" 18 bit 920, the 920ME

In 2016 I obtained a computer called 920ME from eBay - although quite expensive, the name forced me to buy it in hope
to complete my collection by a 18 bit member of the Elliott 900 series:

[920ME-eBay2.gif]       [920ME-ConditioningLabel.jpg]

The unit with part number 75D28482 contains several PCBs with DIL chips centered around the AMD29xx minicomputer chipset.
The ALU is 18 bit wide and composed of five 2901s. From the date codes the machine with serial number 140 must have been
manufactured after mid of 1982:

To make it a replacement for the core memory based 920M they fitted CMOS ram (two PCBs with 8k of store each) which is
buffered by a battery. Two supplies deliver 5V to logic and memory subsystem and the front side hosts three plugs. One for the loading unit
and the two others probably for a panel (keys, start/stop etc.) and/or memory expansion. Internally
an other two memory PCBs may be fitted giving a total of 32k words of parity checked store:

[920ME-Memory8k.JPG] [920ME-BateryReplacement.JPG] [920ME-16kStore-CompleteMachine.jpg]

Over 6 months I analyzed the plug for the loading unit and fixed some bugs (mainly a bunch of three
defective 54138 chips - all with same date code and a problem in the power supply). A homebrew interface
based on an Arduino MEGA is now interfacing the ME to a modern PC and it is emulating teletype and paper
tape stations. 9 paper tapes are hard-coded into the interface and a 10th can be loaded to the Arduino's RAM;
parity/telecode conversion can also be done by the new interface. As the plugs are very hard to find (RSM07 series),
the connection currently looks quite lousy but it works (any of the male RSM07 plugs are welcome!):

[920ME-LoadingConnector.JPG] [920ME-RunningBASIC-SavageBenchmark.jpg] [920ME-InterfaceFinal.jpg]

After a visit of Terry in April 2017 where we ran tests he kindly prepared, we are now sure, that the
machine does not have the later additions to the command set implemented, so it does not obey the 905 or ATC
instructions, i.e. it especially does not have got floating point or stack operations in microcode. Apart
from this, there are some differences to the classic 920M instruction set in the 15 functions, but details
have to be analyzed: The 920ME is neither a 920M nor a 905 or ATC.

What makes the 920ME very interesting: There is way more software and documentation available for the
18 bit machines than for the smaller 12 bit ones like PEC. Andrew Herbert collected nearly everything for the
900 series machines what survived the decades and his archive is hosted by the Computer Conservation Society (CCS).
Among Algol, which is also part of my simulator in the next chapter, there are Fortran, BASIC and CORAL out there.

As I final test for the ME I ran the Savage benchmark, I ran on the PEC in 2011, now on the "ME" using the
900 BASIC I obtained a license from Terry. Here is a comparison of the accuracy of various test candidates...

...showing, that the floating point implementation within the 900 BASIC is much better than the MECSL
floating point library available for the 12 bit machines, but it is also slower as the 900 BASIC is optimized for extremely little
memory usage and not for speed (It can be run in only 8k of store!). Together with the fact that the ME is throttled to 920M speed
(or should I write "slow"), the run time on "ME" is comparable to the following "machines": HP-15C, Psion XPII or a HP-41CX.

8. Simulation for 12bit and 18bit Elliott machines

Software development for the 12-bit Elliott machines was often done on the bigger
18-bit machines (903, 920,...). For these Elliott 900 series of computers there
is a fascinating emulator initially written in 1983 by Terry Froggatt to run on VAX and
later on DOS using Meridian Ada. Afterwards it has been slightly modified and improved by
Don Hunter, who fixed a bug and added support for the plotter and many examples for
the included Elliott Algol compiler. The DOS version (with and without plotter
support, source, manuals and with lot of examples) can be found on Don Hunter's page
as a SIM900AL zip-file.

Since I wanted to learn more on Ada, the Elliott 900 and since I love my SGI/IRIX boxes, I recently
ported this great emulator to gnat using GtkAda for the plotter emulation. This one runs on UNIX
operating systems (Sun, SGI) and on Windows 2000 or later. No Installation required!

Starting the emulator, the mission of Apollo8 around the moon is simulated. This
example for the Algol compiler must be from around 1964. The starting parameters of
the mission can be modified by editing the file ElliottIn.dat with an arbitrary text
editor. The first numbers on the last line in this file are starting height and speed.
Changing e.g. height from 300km to 305km you will observe a disaster happening at the end.

Keep in mind, that the Sim900al-NT runs many times faster on a decent PC or workstation
than on the original Elliott 903 or 920.

Download the latest version 1.3 of the emulator here, now containing all of Don's Algol examples,
the source code and two utilities (one for converting paper tapes from 903 telecode to ASCII and
another to view the headers of tapes - thanks again to Terry):

Architecture/OS Version/Distri/HDD Comment Link
MIPS/IRIX 1.3/3M5/12M7 UNIX-Versions: Extract the tarball, cd to the generated directory and execute the bash script Sim900al-NT. This script will set the required environment variables and launch the architecture dependent binary afterwards. Read file readme.1st. DOWNLOAD
SPARC/Solaris 1.3/5M8/19M0 DOWNLOAD
x86/Windows 1.3/1M6/4M8 Extract the zip file and directly start the Sim900al-NT.exe to launch the simulator. For more information read the file readme.1st.txt. DOWNLOAD

Currently Peter Onion, who is working on the restoration of a 903 and who already wrote an
emulator for the 800 series Elliott computers (bit serial machines), is thinking about writing a new
simulator with fancy graphics and real-time behaviour for the linux platform. Visit his page here:


Additionally there is a new 900 series emulator written recently in F# by Andrew Herb.

A very interesting fact is, that although there is no direct emulator for the 12 bit machines like PEC, these machines can be
emulated as well: An emulator running on the 18 bit machines called SIM can be used to run 12 bit code (including initial
instructions) on any 18 bit 900 series machine and especially within my simulator. So to work with 12 bit Elliott code
on modern hardware, a two stage simulation works very well
; Compiling 12 bit software can be done
using a single stage simulation using the cross assembler EHB directly within the 18 bit simulation.

9. External information...

...For more detailed information, please look at the following threads on the usenet or follow the links given:

And some related information/threads:


...to the people who contributed by answering to my questions in the above mentioned threads, by supplying information or just by listening or being interested in this project! Special Thanks to the following great individuals: Terry, Chris C, Chris B, Don, Andrew, Rob, Peter, Adrian, Frederic, Rod, Roger, Christopher, Simon, Alf, Tony, Kevin, Brian, Ian, Benjamin. But the journey is not yet finished, thus...

11. Items/Information wanted...

During my work on the PEC, apart from reverse engineering, I did a lot of research on the "origin" of this unit
and the applications similar computers probably have been used. Here searches on the Internet and reading
many books and watching available DVDs on Tornado and Nimrod where very helpful. Additionally I did
research (either by inquiry or in persona during one of my visits in the UK) at various UK based Museums
(e.g. RAF Museums in London and Cosford, FASTA  in Farnborough, Rochester Avionics Archives (RAA),
Science Museum in London and last but not least MOSI  Manchester).

The result are some parts with NSNs and/or part numbers I'd be interested in. If you have any of those or if you are
interested in discussion and/or have any information on those than please feel free to contact me at erik@baigar.de!

Download list as XLS-File-V1.7!        (Old Versions 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 and 1.6 )

Programs have been loaded onto early Elliott computers using paper tape. For this purpose an unit called "Program Loading Unit" (abbreviated PLU) existed where the paper tape itself was enclosed in cassettes. This type of  loading facility was used in various applications, e.g. the early fire control system  FACE  on board the FV432 tank. 

So wanted is one of the following NSNs: 7025-99-574-1264, 7010-99-809-3675 or 1290-99-961-6841 (Part numbers FV860118, MDSD76-66 or FV 2188706).

The cassette with the paper tape shown on the right may also belong to the GPLU (below). These images can be downloaded and magnified.

Later on, an improved version of this box, which still was paper tape based, replaced the PLU allowing many different machines (12 and 18 bit) to be booted - even those machines which did not have a boot loader installed (called initial instructions). PEC is of this type! Due to this versatility this box was entitled "Program Loading And Interface Equipment" alias PLAICE. Although this is the most wanted item I unfortunately do not have a picture of this unit, but it should be according to reference number  T(F)M/187 dated somewhere in 1975 and likely NSNs are 1290-99-225-4526 or 1290-99-826-9627 (Ref. Nos. FV860118 or 2-33-0-201).
Unfortunately I do not have got any pictures, but it probably used paper tape cassettes as the PLU above!
The bigger brother of PEC, being an embedded 18 bit Elliott architecture machine is the 920M, which was widely used in the UK throughout the 1970ties in land, sea and airborne applications (e.g. the Jaguar) and it even was in space onboard the Blue Streak and Europa rockets, where it acted as guidance computer.

One variant of this machine is known via NSN 7440-99-111-8581 and the Rochester Avionics Archives  hold several of these toys (part number something like IL322A11787, MCS.920 or 920M).

Although I already have got a 920ME in my collection, it is always great to have a spare unit in case there is a problem: Coarse search by swapping boards saves a lot of time, especially if no schematics are available! Additionally the store of a second unit would be great to max out the store of my main "ME" to 32k words ;-)   So wanted are
  1. The unit itself, 75D28482 and/or
  2. the control panel 75DSK17611.
  3. Any PCB of the machine is highly welcome as well: 75D28483 to 75D28488.
Around 1976, the technology in semiconductors had advanced significantly, so the successor of the 920M, which was based on DTL chips, was released and called the 920ATC (Advanced Technology Computer). It still had core memory to ensure long data and program retention times.

One of these beasts would be a highly welcome item!
Possible part numbers for processor are 50-031-01, 95-106-01, 95-106-02 or 95-102-01 (related NSN may be 4920-99-760-0485).
The matching control panel (OMP) and/or program loading unit may have one of the following part numbers: 25-017-01, 25-017-02, 25-017-03, 25-017-04 or 90-168-01 (NSN 4920-99-760-0484).

12. Various pictures related to the "Programmer Electronic Control"
and their reverse-engineering (chronological, click to enlarge):

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13. Older history:

21.6.2015: Some more pictures added to the VCFe section and efforts regarding
CVR and RPMD documented - including a 15 min video.
5.5.2014: Another update: VCFe documents now contain the feedback I got.
25.4.2014: Big update with many new pictures and information. Update to the
wanted items lists. Added picture of current setup.
25.9.2012: More pictures and updated logbook with stuff related to
work on WFG1, PEC-OMP and Rolm1602.
26.1.2012: Addition of a "wanted" section listing and explaining
items and information I am looking for (also XLS available).
23.6.2011: Documentation of the progress of the last 4 months: PEC-Sound,
update of the vintage computing and avionics logbook with lot of information
and extension of the PEC picture gallery.
2.6.2011: Smaller release: Version 1.3, with minor change in handling the terminate interrupt
instruction, of the Simulator released (can now run the 12bit simulator within
the 18bit simulator).
12.2.2011: PEC: New version 1.2 of the Simulator for 18 bit Elliott machines released.
Tornado Engine Computer donated to the Deutsches Museum in Munich (TimeLine).
12.12.2010: PEC: Added latest achievements to the Time-Line - included are a short video of the
BlinkenLights, ideas what the panel will look like and an outlook on WFG1.
30.05.2010: Added info on the inverter, the UK-Trip and latest achievements with the new PEC setup.
30.01.2010: Added first blinkenlights related information and pictures of the newly acquired waveform
generator from the early versions of Tornado.
13.12.2009: Latest achievements added to the Time-Line and supplied the "gallery" with new pictures.
6.7.2009: Checked all pages for dead links and removed them; added diary to the "PEC-page.
6.6.2009: Added pictures of latest milestones - plotter is running under control of PEC now.
Pictures sorted chronologically. Added index.
31.3.2009: Added counter and some explanations to the documents from Terry Froggatt.
8.6.2008: Added technical information on all chips, used on the unit together
with date code statistics. Added picture of 902, too.
4.5.2008: Added NSNs, Part-numbers and pdf with pictures of all PCBs.
29.4.2008: Added Elliott 900 series emulator (Thanks to Terry Froggatt & Don Hunter).
28.4.2008: News: The unit is said to be part of the early Foxhunter Ai24 radar
of the Tornado ADV aircraft.
28.2.2008: Added some links (picture 903, time-line).
19.1.2008: Added pdf containing all secrets I prayed out of the box,
box identified as an Elliott 12/12. Probably NOT from Tornado.
5.1.2008: Added pdf files of the relevant threads in newsgroups etc.
7.11.2007: Update with new pictures (Starting with _), including new unit.
15.9.2007: Got second of the units, serial number 129. Both units show same
behavior in all respects. New unit has maintenance sheet attached,
thus assumption is: Both units are OK. ;-)
17.6.2008: Now ALL (even the custom ones) chips in the PEC are identified, thus there
is an updated version of the Reference-Page with pin-outs.
15.6.2008: Added additional Foxhunter picture, both now available in better
resolution. Uploaded new documents about 12/12 and 902 but not
properly included yet - sorry.

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