Video Wall Computer - MTX512S2

The Video Wall Computer

Memotech Video Wall systems were initially made up of a Memotech Z80 computer (an RS128 or MTX512S2) with a minimum of 128K RAM, attached via the printer port to a black box (what else?) controller packed with electronics to drive a wall of video monitors. Some later systems were equipped with the MTX 2000 computer, before the company moved onto the industry standard PC platform.

The photo at the top of the page shows the MTX512S2 computer in my Video Wall bundle, the computer is fully working, but as the photo shows, it is missing key tops for number "3" on the main keyboard and number "4" on the numeric keypad.

The internals of my Video Wall MTX512S2

The Video Wall was available with two different MTX computer configurations, the system described in the Cameron Users Manual consists of an MTX computer and SDX disk drive that was used to load the Video Wall software and to load, edit and save Video Wall sequence programs. Alternatively, the Video Wall software and sequence program(s) could be stored in ROM fitted to an internal ROM board in the MTX computer as illustrated by this photo of my MTX512S2 Video Wall computer.

MTX ROM Board with Video Wall ROMs fitted

A close up of the ROM board in my MTX512S2, showing two ROMs labelled "G/ARMS 1" and "G/ARMS 2".

Originally written to provide a low cost way for users of the Memotech SDX to run CP/M without requiring an 80 column board to be installed in the MTX, Andy Key developed software to configure the TMS9929A VDP to have a 56 column text mode and integrated it with the CP/M boot ROM to produce a 56 column bootable ROM known as an "SCPM" ROM. Whilst the 56 column mode would likely not have been comfortable to use, in Video Wall applications, it was only used during the CP/M boot before the 40 column Video Wall software was loaded. To allow a Video Wall system to operate without a disk drive, the software needed to be copied from ROM to a RAM disk, this was performed using code from a "RCPM" ROM which did the ROM to RAM copy.

The 2 x 64 kb ROMs on the Video Wall ROM card contained the code for an 8kb boot ROM, a hybrid of the SCPM and RCPM ROMs, called an RSCPM ROM, the Video Wall executable and sequence programs. Full details of the Video Wall ROM configuration, including SCPM, RCPM and RSCPM descriptions can be found on this page on Andy's site.

The component side of the 4000-04 computer board

The Video Wall software needed at least 128kb of RAM on the MTX computer board for the RAM disk, requiring either an RS128 computer (128kb RAM) or an MTX512/MTX512S2 with 256kb of RAM. The photo shows that this MTX computer board has had its original 64kb RAM chips upgraded to 256kb, the solder side shows the "yellow wire" modifications required to allow the CPU to "see" the additional memory.

A number of advanced Video Wall options such as time code synchronisation, mouse control, operation of the "Reflex Touch Controller" etc, required the presence of an RS232 board in the MTX. The "Reflex" controller used the RS232 interface to allow the operator to quickly select any of the available pre-programmed video wall control sequences using an attached mini-keyboard.

The board above is the MTX500 - RS232 / Interface board originally used to connect an MTX computer to an FDX disk drive system, used here to provide the Video Wall system with RS232 ports, the FDX interface chips have not been installed.

After booting CP/M, the STARTUP command executes "VW94 F8\F3\F1\"TOBY"\F8\F8\F5\"RUN"

The Video Wall Product Description and the Cameron Users Manual helps us decode the meaning of the start up string :

This would automatically start the default Video Wall sequence, but the keyboard could be used to make changes as required, although any changes to configuration etc. would be lost when the Video Wall computer was reset or powered off.