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The Memotech MTX Series


     Multi-Effect Video Wall    


The Distributed Digital Frame Store (DDFS)

The heart of the Memotech Video Wall system is the Distributed Digital Frame Store (DDFS)


The Video Wall operator interface, typically a Memotech MTX computer, is connected to the Video Wall DDFS controller(s) using a 34-way ribbon cable between the operator interface parallel port and the IDC sockets on the rear of the DDFS.

Each DDFS has two IDC connections - one for each Frame Store Controller Board (see below) and two RGBS connections to the Decoder/Distribution Amplifier, again, one for each Frame Store Controller.

(See my Video Wall Overview page more information on how the components of the Memotech Video Wall system are assembled.)

The major components in the DDFS are :-

Memotech badged Video Wall systems were available in two versions - the medium resolution (mid-res) Memopix 1500 (DDFS 1.5) and the high resolution (hires) Memopix 2000 (DDFS 2.0). Both systems were capable of 128 independently programmable modes per monitor but the DDFS 2.0 Frame Store boards had 4 times the memory capacity of a DDFS 1.5 board which gave the Memopix 2000 system better resolution and additional special effects such as distortions, mirror, inverted and picture-in-picture features.

Cameron badged Video Walls were also available in two versions - called System 100 and System 200, although the Cameron User Manual only gives a single set of specifications, it is assumed that the difference between the System 100 and System 200 was also in the amount of memory on the Frame Store Memory Boards.


The DDFS rear panel, showing :-

2 x 15 way ""D" connectors for the RGBS inputs from the Video Decoder

2 x 34 way IDC connectors from the MTX Centronics interface

12 x 9 way "D" connector panel (9 used) for the RGBS video outputs

Internal view from the front of the DDFS; in addition to the PSU (on the right), the DDFS houses two 6" card files.

Connections to the rear panel connectors are made using the ribbon cables visible at the front of each PCB.

A close up of the left hand card file, the upper five boards are the Frame Store Memory Boards. Each FSMB connects to a dedicated monitor via the small ribbon cables to the 9-way "D" connectors on the rear panel.

The lower board is the associated Frame Store Controller Board ; the 34-way ribbon cable connects to the MTX computer via the 34-way IDC connector and the 15-way ribbon cable connects to the RGB input 15-way "D" connectors - both on the rear panel.


Frame Store Controller Board (FSCB)

Up to two FSCBs can be installed in a single DDFS and each can control up to five Frame Store Memory Boards (FSMB).


You can see that the FSCB is pretty much laid out in two halves.

On the upper half of the board, each colour of the RGB video signal fed to J2 is amplified by a UA733 video amplifier and then digitised by a CA3306E 6-bit A/D converter before being made available to the frame store memory boards through the backplane.

The lower half of the board is associated with the command signals fed to J1 from the computer which are then processed before being made available on the backplane.

Memotech schematic for the FSCB - Mark II Version (1988)

This is a later version of the board than installed in my Video Wall hardware and includes a Plessey SP94308 8-bit Video DAC which replaces the UA733/CA3306E Amplifier & ADC components used in the earlier board.

Courtesy of Tony Brewer

To be continued . . . . . .


Frame Store Memory Board (FSMB)

Communication between the FSCB and the FSMBs is via the back plane of the 6" card file, as the card file has a total of six slots, each FSCB can control up to five FSMBs. Therefore a single DDFS can control a maximum of 10 monitors and larger Video Walls were built using additional DDFSs as required, up to a maximum of 8 giving 128 monitor outputs.

Unfortunately, my DDFS is the med-res version using DDFS 1.5 boards having 16k x18 RGB bits per frame store. DDFS Version 2.0 boards have 64k x18 RGB bits per frame store.

As the name indicates, the FSMBs stored and manipulated the image data.

The 18 SRAM chips on my DDFS 1.5 boards are ST 2167-55Ns, below each column of RAMs is an empty location for an additional RAM chips for each colour which would have allowed for 7-bit video, but as the A/D convertors on the FSCB was only 6-bits, there was no point in installing the extra memory chip.


To convert the video information back to analogue RGB, there are digital-to-analogue converters adjacent to the 9-pin "D" connector - J1.


As Geoff Boyd recalls, "these use a [Memotech designed] custom resistor network and AC574 (HC574s worked as well) to make a Video speed DACs. That was a trick we kept up our sleeve, together with using tri-state AC244s and a PAL (ULA) to do variable RGB output filtering and colour washes. It gave us a competitive edge by making the product highly affordable because high quality triple video DACs in those days costs upwards of 50 pounds each compared to less than a couple of pounds for the entire DDFS RGB output solution."

To be continued . . . . . .




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