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The Memotech MTX Series

Memotech Compact Flash System

CFX - Special Fit





 
MTX CFX Boot Screen





 
CF Card Directory

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Introduction

The CFX ROM includes a version of Andy Key's SCPM ROM which enables CP/M to run on a Memotech computer without the need for an 80-Column card; the MTX VDP was used to generate a low quality 56 column text mode. However, CP/M needs 64k of RAM to run on the MTX, users with a 32k MTX500 are not able to run CP/M without increasing the RAM in their machine.

There are a number of options for upgrading an 32k MTX to 64k, including :

  1. Install an original Memotech RAM expansion card - though they are hard to find

  2. Remove the existing RAM and replace with 64k RAMs - requires de-soldering the existing RAMs

  3. Install one of Andy's Memotech RAM expansion boards - would require CFX to be installed externally

Option 1 is not really viable unless you already have a spare Memotech memory board and, depending on your skills with a soldering iron, option 2 can be risky. The easiest option is 3, buy one of Andy's RAM expansion boards. Since neither Andy or my expansion boards replicate the "finger" edge connector of Memotech's PCBs, the typical way to do this would be to install Andy's RAM card internally and CFX externally, though the positions could  be reversed if you wanted.

After purchasing CFX, one buyer found that his "MTX512" had a 32k computer board inside, but it did not have the 32k RAM expansion board that Memotech supplied inside many machines with a 32k computer board to make them into 64k/MTX512 machines. Since the buyer didn't want to take the risk of damaging his MTX by trying to replace the computer board memory, but wanted to add more memory AND install the CFX board internally, I worked up a solution using a mating pair of DIN 41612 connectors.

 

The PCBs and backplane in MTXPlus+ use 2 row, 64 pin, DIN 41612 connectors.

By removing the top two rows of pins, it was possible to use these connectors to join one of Andy's memory cards with a CFX board and install the two internally.
As you can see from Andy's circuit diagram and the schematic for CFX shown here, neither board passes the full compliment of the Memotech expansion bus signals over the PCB.

Andy's board doesn't use the ROM select signals (R0 to R2) and CFX does not use the RAM select signals (P0 to P3), so, depending on which board was installed closest to the MTX computer board, a number of patch wires are needed.
I thought that the RAM board was best located next to the MTX computer board, so I patched R0 to R2 between the edge connector terminals in true Memotech style - using yellow wires.

The finished boards, with a DIN 41612 female connector on the RAM board and male connector on the CFX board.
Underside of the boards
The board connected and installed inside the MTX case.

As you can see, there is ample room  for the PCBs, but the CFX adapter must be mounted externally.
The result !

Note the 64k of RAM reported on the CFX boot screen. Despite the "MTX512" label, this MTX has only 32k of RAM on the computer board, the other 32k is being provided by Andy's RAM board.

The CF card reader is attached to the CFX board with a 40 pin ribbon cable that exits the case through the FDX interface cable slot.

 

 

 

References:

1 Andy Key's Memotech Hardware page

2 Que Publishing, Upgrading and Repairing PCs, 21st Edition, ISBN-13: 978-0-7897-5000-6. Sample Chapter : The ATA/IDE Interface

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