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ICL One Per Desk

 One Per Desk 


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Technical Info


ICL One Per Desk


The ICL One Per Desk Computer (known as the OPD) was released in late 1984 / early 1985 and was based on the Sinclair QL Home Computer, and included improved ZX Microdrive units and a built in telephone and modem, phone directory, speech synthesizer and Psion Xchange on EPROM.  It was also released under the name Merlin Tonto for BT and the Computerphone for Telecom Australia (APT).  There were even a few machines released for North America.

The links between the OPD and the Sinclair QL relate mainly to the hardware, with the same 68008 CPU, the two main QL ULAs (the ZX8301 and ZX8302) and the built-in microdrives - the same method of RAM and screen management was also implemented, although most QL software will not run on the machine.  As with the QL, the One Per Desk included 128K of memory (with 32K being used for the screen), but also included an extra 2K of battery backed CMOS RAM.  It appears that the maximum memory that could be added was a further 128K (giving total 256K RAM), compared to the Sinclair QL - however, as it was planned for the majority of software to be provided on ROM (for immediate loading), this is not too much of a problem.

A ROMPACK was released for the computer, which could have either 2 slots or 4 slots and this was used to good effect to provide Psion Xchange 2.5 in either a 1MB PROM (the XFAA01) or 256K PROM (the XBAJ02).  Another option which came out of this was the release of the ICL 128K Memory Expansion  Unit (MEU) which included Psion Xchange 2.5 and firmware for a slow RS232 port included on the MEU.

Another 128K memory expansion was provided by PCML (the Telestore).

More technical details on the ICL One Per Desk hardware appear at Binary Dinosaurs in an article by Murray Macabe.

The Operating System was different to the QL's QDOS, although it did allow multitasking, part of it was based in the ROMPACK.  Standard software was provided built in, as follows:

KERNEL - manages the hardware, the memory map, input output device control, and also handles interrupts.
DIRECTOR - is higher level firmware handling applications and the telephone. It controls START, RESUME and REVIEW key functions and allocates resources.
TELEPHONE HANDLER - manages the 'nuts and bolts' of telephone usage.
TELEPHONE DIRECTORIES - 2 directories are managed, one for telephone voice calls and one for computer services.  It can handle over 500 entries, but this has to be balanced with memory requirements.
CALCULATOR - A simple 16 digit calculator with memory (the CALCULATOR firmware is in the ROMPACK).
SCREEN IMAGE PRINTER - A screen dump to printer on a single keystroke.
FIELD EDITOR - provides cursor and text editor control.



The following hardware was developed for the ICL One Per Desk

The ACU was designed, by ICL, as part of the MEU expansion system and offers speeds of up to 19200 bps by, optionally, by-passing the OPD's integral modem, so allowing high speed communication and networking under control of one of the terminal emulation programs. Canadian Standards and ULA approvals were obtained and the unit was still available from ICL, in early 1988.

This unit's program is called a LOCAL COMMS. CONFIGUPATOR and allows profiling of port parameters and operation by ACU or by modem. The ACU was designed to compliment the MEU, was contained in a steel case approximately 4.5"x 10.5"x1.5" and powered from the OPD, either direct from a ROMPACK slot or, alternatively, it could sit on the MEU fed from that unit's 60 way expansion port. The ACU 'footprint' is the same as the TELEDPIVE's.

The ACU has a single 25 way D connector, RS232C port based on an 'intelligent', Intel P80C31BH processor with a 7.37280 Mhz crystal. A series of 74HCT257 multiplexers allow control to be taken over from the OPD, by the P80C31.
Firmware is provided in 2 EPROMs (a 27C256 and a 27C64). A small ASTEC encapsulated SMPS is 5 powered from the +5 voLt rails to generate standard RS232C port voltages which are not available via the ROMPACK slot (i.e. +12 and
-12 volts). Two 2K CMOS RAM ICs provide buffering for data. Transmission and reception speeds can be specified separately in the range from 50 to 19200 bps. Other adjustable parameters are word length, parity, input and
output buffer sizes buffer filling and emptying levels, X-ON and X-OFF and flow control.

Profiles/patterns for various port configurations can be set-up, stored in the OPD PERMANENT STORE and recalled for particular applications.

This was a free standing, self-powered unit that works with VT-LINK to provide OPD to IBM mainframe communications. Full screen working to the IBM host is available at speeds up to 9600 bps together with access to the host's applications. Security features are included with auto-answer from the OPD.

This was provided for the Tonto by BT. It connects via a ROMPACK capsule slot, is powered from the OPD and provides outputs (via a 25 way, female D connector) which are compatible with RS232C, RS423 and CCITT V24 standards. Emulation of the following terminal types is possible: DEC VT52 and VT100 (80 column mode only) and IBM 3278 via a suitable protocol converter. Baud rates from 50 to 9600 can be configured from software. 2400 is the recommended rate.

This provided simultaneous voice and data communications on a single telephone line.

This was a free standing, self-powered, adaptor for connecting OPDs, running ICL-LINK, to ICL SME or TME mainframe computers at speeds up to 9600 bps. Full XEM (ICLC-03) terminal emulation is provided with dual screen capability and auto-answer from the OPD. The DTCU microcode (E13100/01) is teleloaded from the mainframe.

This allowed you to connect the OPD to ICL DRS series computer systems via DRS model 110.

ICL One Per Desk with MEU (Memory Expansion Unit) under TeledriveICL Memory Expansion Unit (the MEU)
This was a 128K expansion unit and was intended to be the main unit of an ICL expansion system. It had a slow RS232 port (for bar code reading, printers etc.), 4 capsule slots, a RESET button and a 60 pin expansion port. The MEU was large, approximately 10.5"x 7.2"x 1.5". The case was steel with a plastic overcover and it connected to the One Per Desk via a 6 inch length of ribbon cable and a modified ROMPACK case containing line drivers and receivers.

The MEU memory duplicates the basic arrangement in the OPD and is controlled by a ZX8301 with a 12Mhz crystal. The address lines to the ULA are modified to position the memory at the expansion addresses. Two 74HCT2S7s provide DRAM address multiplexing and a 74HCT245 acts as the data bus transceiver. The memory itself uses four 256K DPAM ICs (81464 devices, each 64Kx4 bit).

Inside the ICL One Per Desk MEU (Memory Expansion Unit)XCHANGE version 2.5 is included in the unit, provided in two PROMs. A third ROM, a 27C64-25 EPROM, carries firmware to initialise the new memory and service the RS232 port.

As this was bulky and expensive, it was soon superseded by the PCML TELESTORE unit.

This allowed files to be transferred between OPDs and IBM PCs.

The Mega Capsule is an extended Capsule housed in the case supplied for cable connection from the Rompack to the Teledrive or ACU. Inside, an enlarged PCB carrying 2 x 27512 EPROMs, a small capacitor and an HCT04. The Capsule utilises memory paging techniques to handle the extra EPROM Space.

The Ramcap is of much later design and consists of a bank of four HM66202L-15 surface mounted Ram chips backed by a 3v Lithium battery.

On one side is a small slide switch labelled Write protect - Write enabled. This unit was employed for the development and testing of software. It is possible to load software into the unit, reset the OPD and test. The unit also makes software (not yet in EPROM) to be ported to different versions of the OPD for compatibility testing.

This allowed the OPD to be used as a Telex station

This was a security device produced by PCML. It consists of an in-line plug/socket assembly which plugs into the 2 'D' connectors on the OPD control unit (the supplies/video and the printer connectors) and provides 2 new 'D' connectors, at
its outboard end, for the original leads. There is a lock on the unit operated by a Yale type key. The OPD can be disabled, for security purposes by locking and removing the key.

TELESTORE Memory Expansion
The PCML 128K memory expansion, TELESTOPE, fits into a ROMPACK case. The original version had 4 'slots' plus version 2.5 of XCHANGE. A later, 1987 version, was built into an extended case and accommodated 6 capsules.

PCML designed the TELESTORE with a fairly standard ROMPACK base board plus a 'piggy-back' board containing the extra memory. Unlike the standard ROMPACK the main components are soldered into the board to cut down height and allow the assembly to fit into the standard case. The 'piggy-back' memory board is mounted on a 34 way, in-line header strip.

The 128K memory is 4 off 4464 ICs (64K x 4 bit each), controlled by a Toshiba TC17G014AP-12 CMOS gate array which is custom programmed and uses a 12 Mhz crystal. The 'piggy-back' board also contains two 74HCT257 address multiplexers
and a DIL resistor network.

The base board contains 2 PLA devices, buffers and XCHANGE 2.5 in two ROMs. The ROMs are the ICL/PSION XFAA01 and a 27C512 EPROM containing the remainder of XCHANGE plus the initialisation firmware for the extra memory.

Both the MEU and TELESTORE included special initialisation and checking firmware for the memory expansion. When an OPD is powered-up with TELESTORE (or the MEU connected) the screen displays that an 'Invalid Capsule' is present and
HOUSEKEEPING shows the standard free store capacity of about 150 blocks. The special initialisation routine then checks and logs-on the new memory and the updated HOUSEKEEPING Store Report shows the increased memory of about 400
blocks. This extra process takes about 15 seconds and does not cause illumination of the line LEDs, as in the normal initialisation.


We have started a project to resurrect a disk drive for the ICL One Per Desk and derivatives - see our page on ICL One Per Desk Storage Solutions.


The following software was released for the One Per Desk computer:

A program for creating special spreadsheet templates for income tax, budgeting, financial reports etc. by Patrick and Leach.

Satellite Computing produced an ACTION DIARY.

An upgraded version of ACTION DIARY from Satellite Computing

An expansion of MESSAGING which occupies 2 capsule slots, providing all the facilities of Messaging plus auto-retry; multiple addressing and an interface facility with EXPORT format files.

A program to simplify basic ARCHIVE application which the user can then tailor to his individual needs. It requires XCHANGE vers. 2.5. and was available from Ark Distribution.  This program was also released for the Sinclair QL.

This also was from Computer One and intended for release as a special ROMPACK assembly. XCHANGE was not available with this ROMPACK but the system included an editor for program preparation. The Compiler and Interpreter were Microsoft compatible and provided performance improvements of 3 to 4 over OPD Basic.

A Satellite Computing Romcap linking Basic programs and the telephone.

A program from Control-C Software for jotting down ideas which can be refined at a later date.

A 3 capsule set from Computer One was scheduled for release in mid-1986. The Compiler was in 2 capsules and the Assembler in one. These were to be supplied with a 4-slot ROMPACK containing XCHANGE with QUILL being used to prepare and edit programs.

This was available from PSION for the OPD with 28 levels of play.

Combines the functions of ICL-LINK, VT-LINK and TERMILINK in a single capsule. This is incompatible with VT-LINK 2. If both are fitted to the ROMPACK at the same time the OS will log-on only the VT-LINK * program with the lowest memory address.

Metacomco supplied a cross-development package which allows OPD software to be developed on an ICL or IBM PC.

DATALINK (BT Reference M1824)
A single capsule introduced to overcome, in part, the isolation of the XCHANGE programs from the communications facilities. It allows incoming communications data (from a computer service or mainframe) to be imported to XCHANGE. It also allows QUILL format files to be exported by the communications facilities of the OPD.

A Capsule from MGB Micro Products which allows the OPD to auto-log-on and auto-answer when used in conjunction with the MGB Dialback Security System.

ICL - DEMO (BT Reference M1853)
A demonstration program for XCHANGE including a '.dbf' file on geography for working through ARCHIVE.

Occupies l capsule slot, allowing communication with ICL mainframe computers and emulation of a full XBM Screen Mode Terminal. ICL-LINK requires a Desk Terminal Connection Unit (DTCU) for the link interface.

BASIC is not resident in the OPD. It is loaded from microdrive and is a subset of Sinclair QL SuperBASIC. It lacks SuperBASIC features especially graphics such as LINE, CIRCLE and ARC. In multi-tasking, there is insufficient memory to store several complete graphics screens and recall them with the RESUME and REVIEW keys.

ICLBASIC was intended as a high level bridge to QL software but, as such, it has limited capabilities. BASIC version 07 was available in 1986. The version in use can be displayed by the PRINT VER$ command. The early Basic versions included features which were discontinued in later versions e.g. Ver. 5.02 includes Tokenised SAVE and PUBLISH commands TK_SAVE and TK_PUBLISH respectively. These allow Basic programs to be saved in a coded form with a table of keywords and commands. This increases the length of small and medium files but can reduce programme loading times by factors up to 3 (and are similar to the QL's QLOAD software).

The BASIC cartridge contains the factory-set default values of the PERMANENT STORE plus configuration programs for the OPD, the printer and the telephone (CONFIG, CONPRIN and CONTEL respectively).

ICL/PSION - HELP (BT Reference M1854)
HELP files for the XCHANGE programs are provided as a microdrive cartridge.

ICL WELCOME (BT Reference M1850)
This cartridge was supplied as part of the WELCOME package to provide information and to demonstrate the equipment's capabilities to the new user.

ILLUSTRATOR EGO (Executive Graphics Option)
Occupies 1 capsule slot, allowing connection of an QPD to an ICL mainframe (via ICL-LINK, and a DTCU ) to view professional graphics on the OPD. Graphics may be viewed and stored on microdrive but cannot be altered or edited by the OPD.

INTERFILE (BT Reference M1823)
Occupies 1 capsule slot allowing file transfer from OPD-to-OPD via the modem. Facilities include auto-retry and transmission at pre-set times. The INTERFILE ROM includes 'patch' code to permit more than 6 ROM applications to be connected to the OPD at the same time.

Another implementation of Basic for the One Per Desk produced by MetaComCo for American versions of the computer. Originally in a Mega Capsule, it was later available for installation in a standard 2 slot ROMPACK. This version of BASIC was more compatible with early Basics such as GWBasic and MBasic starting with the familiar 'Ok' screen prompt - however, enhancements were made to make it compatible with both ICL Basic and Microsoft Quick Basic.
This Basic forms part of the system for use with the Basic Compiler for the OPD.

Programs are written and tested in Basic then compiled.

Some documentation available.

Better BASIC Quillinan, (Butterworth, 1985)
The MBASIC handbook Ettlin & Solberg, (Osbourne/McGraw Hill 1983)
MC BASIC Reference Manual , (Metacomco plc 1985)

Originally consisted of a Mega Capsule only intended for use with the later version of the OPD bound for the USA. The Mega Capsule employs memory paging techniques that are incompatible with a standard OPD. However, the program has been copied to 4 x 32k EPROMs and can be inserted into a standard 2 slot ROMPACK.

The package was written by Computer One and consisted of:
MC Basic Compiler
68008 Assembler

The menu also lists a linker, but it has been confirmed that this section was never completed.

The compiler output carries a large overhead of library sub-routines making small applications uneconomic in terms of memory. Once past the 'threshold', however, larger programs are most suitable. Should a suite of programs be running together, it is necessary only to load the library once. An option exists at compiler run time to exclude the library.

Alas, no documentation is available which covers the OPD version of the Assembler or Compiler.

Although officially required to compile MC Basic, many of the features of ICL Basic for the OPD (itself a variant on the Sinclair QL's SuperBASIC), are included in tandem. This gives access to the superior features such as user defined Procedures instead of position dependant GOTO and GOSUB.  The compiler also has the ability to compile Basic lines that MC Basic rejects, for example the command line(x,y)-(a,b) is rejected by MC Basic but can be compiled and actually allows the user to draw a line on screen, despite the fact that ICL BASIC does not contain any graphics commands!!

The compiler writes a run-time library for each program that takes up about 20k. Small programs will therefore occupy relatively more space. Medium to large programs will save space due to the re-using of library routines. The main advantages of the compilation of the program is in speed of execution, memory usage (there is no need to load Basic), and the ability to choose the program from the Application's menu.

Some documentation is available but no 'official' handbook was written.

MESSAGING (BT Reference M1821)
A single capsule which provides desk-to-desk text messaging between OPDs; unattended receipt; auto-send; dump to microdrives and a print or resend option.

A capsule from MGB Micro Products including all the facilities of DB-LINK plus the ICL-LINK terminal emulation package.

A business forecasting program from Control-C Software.

Superplant Software offered a database system which uses ARCHIVE to help with tree and plant selection and care.

A cut down version of WordStar for use with the TELEDRIVE disk unit running CP/M.

A Satellite Computing Romcap providing a graphics display system for producing transparencies and designing, and running, flipchart style presentations using a rolling, on-screen display.

This was produced by Satellite Computing.

These were written by Dave Walker and consist of a QL/OPD FILE INTERCHANGE program and a QL/OPD DIRECT I/Q
TOOLKIT. The same author produces the MultiDISCOVER program which allows disks to be interchanged between the QL and PC compatibles and can even be used to allow the QL to write to disks that the TELEDRIVE can read.

A computer access page store with enhanced facilities including archiving, organising and merging of stored pages and self-running displays.

Provides terminal emulation for the ICL 6402 and 6404 QUATRO series desktop computers.

A small business accounting package from A.M. Programmers.

Produced by Computer One.

VT-LINK/VT-LINK 2 (BT References M1825/M1826)
Occupies 1 slot and provides terminal emulation for communication with Digital Equipment Corporation (DEC) VT series computers. VT-LINK covers VT52 and VT100 emulations. VT-LINK 2 covers the VT52, and VT102. Its manual states it also  covers VT100. VT-LINK 2 includes an improved printer configuration program CONPRIN allowing condensed 132 column printing in some applications. This CONPRIN can conflict with the disk based CONFIGURATION programs supplied for TELEDRIVE.

This was a standard suite of business programs released by PSION in various guises.  It was available for the Sinclair QL as four separate programs originally (Quill - word processor: Archive - database: Easel business graphics and Abacus - spread sheet), and as an integrated suite for the ICL One Per Desk as XChange and as PC Four for DOS based computers.  The integrated package included several enhancements over the original individual programs, including the TSL Programming Language which allowed you to create a program to control XChange.  Xchange has since been made available for the Sinclair QL, with the permission of Psion.

Thanks to the BT archives, we have also received permission to make the notes from an Xchange Training Course available, which may be of assistance to some users.

On the One Per Desk, XChange is provided in ROM, as an option, and mounts in the ROMPACK. Version 2.5 was in service by mid 1985 but surplus units are generally the earlier version 2.3 (the version number is displayed when entering XCHANGE from the APPLICATIONS menu).

In general the 2-slot ROMPACK has version 2.3 and the 4-slot ROMPACK, TELESTORE and the MEU have version 2.5.


Century Communications Ltd. (Newtech Publishing Ltd.) produce 3 guides to the 'Merlin-Tonto' at a listed price of £12.95 each. These books are user orientated and contain no significant technical detail of the internals of the 'Tonto'.
They are:
"Business Communications with the Merlin Tonto" by Martin Gandoff ISBN 0-09 1681-6
"Introducing the Merlin Tonto" by Garry Marshall ISBN 0-09-161661-1
"Business Computing on the Merlin Tonto" by Stephen Morris ISBN _0-09-161671-97

The following user manuals were provided by ICL or BT:

Advanced Messaging
Advanced Operations
(BT Reference TPU 12G)
Basic (BT Reference TPU 12C)
Combined Comms

EGO Illustrator
(Leaflet only)
Exchange quick reference (BT Reference TPU 192)
Handbook (BT Reference TPU 12B)
Installation (BT Reference TPU 12A)
Installing Telephone Lines and Sockets (BT Reference TPU 12H)
Interfile (BT Reference TPU 428)
M1880 Printer Manual (BT Reference TPU 249)
M1881J2 Printer Manual (BT Reference TPU 332)
MERLIN TONTO Some Questions and Answers
Messaging (BT Reference TPU 12D)
MP1887 Datacomms Adaptor (BT Reference TPU 116)
OPD VT100 LINK (BT Reference TPU 334)
OPD Programmers Manual (ICL - approx 700 pages, complete with development ROM)
OPD Serivce Manual (ICL - Details unknown) 
Using MP11881 With Tonto (BT Reference TPU 439)
VT-LINK 2 (BT Reference TPU 730)
Welcome Package (BT Reference TPU 12F)
Xchange (BT Reference TPU 12E)
XCHANGE Quick Ref. Card (BT Reference TPU 242)

ICL also issued a supplement giving guidance on interfacing various printers to the OPD. It detailed the parameters to be set by CONPRIN and which features of the standard OPD/OKI package are not available with other, identified printer types.

A supplement was issued on MESSAGING giving greater detail of error messages and expansion of information on turning the T-LINK protocol on and off.

We would welcome copies of any of these manuals or the ability to make them available once again.


One of the main problems which One Per Desk users face is finding a compatible printer.  The One Per Desk uses a 9 pin RS423 port which is RS232 compatible for use with a printer - it is one way only. Unfortunately, modern printers are unlikely to be compatible.  As more and more printer manufacturers strive to reduce costs by removing components, they presume that computer users have a Windows or MAC based operating system which will translate all text into the graphics code for them.  As a result many printers no longer support a parallel or serial port (which is required by the OPD) and do not allow text to be sent to the printer direct.

If you want to use a standard centronics (parallel) printer with the One Per Desk, you will need a serial to parallel converter.  Alas we have not managed to get any of the standard ones to work and would have to rewire a Sinclair QL converter.

About the best supported printers are those manufactured by HP and Epson, although you have to be extremely careful about which model you have - a full Epson ESC/P2 or HP PCL-4 control set are required for the One Per Desk to fully support the printer.  About the best inkjet which can be obtained fairly reasonably and is fully compatible with the OPD for text, has to be the Epson 850 or Epson 900 printers.  

We can sometimes provide compatible printers and serial to parallel converters second hand.