Memotech Multi-Function Expansion System

MFX

MFX Boot Screen

SD Card Directory

Introduction

Intended to be a development of the CFX range, Martin and I were planning to develop a CFX-III. This was envisaged as a minor development of CFX-II, intended to improve the quality of the graphics output. Whilst CFX-II worked well, the VGA output was not all that I had hoped, with some "noise" being displayed on some, but not all, VGA monitors.

For various reasons, Martin and I rethought the aims of the project and decided that, whilst a Compact Flash based solution was still a possibility, the waning popularity of CF, the increasing prices of CF cards and the lack of a built-in CF interface on most PCs meant that SD card was really a better option and a "CFX" name was no longer appropriate. Given that the simple IDE type interface used to communicate with a Compact Flash card was not going to be suitable, and taking inspiration from REMEMOTECH & REMEMOrizer, it seemed logical that an FPGA device should be used. 

We have now developed a different expansion board for the MTX which includes additional functions and have released it as the Memotech Multi Function eXpansion card - MFX.

 Credits - In advance . . . .

Andy Key's awesome REMEMOrizer deserves a mention at this point. REMEMOrizer was the first SD card expansion for the Memotech MTX with extensive development work having been done by Andy to clone MTX functionality using a low cost FPGA development board incorporating a Xilinx XC3S500E Spartan 3E FPGA. The GODIL development board that Andy used now appears to be out of production and Andy has no plans to make any more REMEMOrizers, so an alternative SD card solution was needed. REMEMORizer was itself a development of Andy's REMEMOTECH, the Re implementation of a Memotech computer entirely in an FPGA development board - the Altera DE1, built around an Altera Cyclone II 2C20 FPGA.

The firmware in MFX draws heavily on the code published by Andy and thanks are due to him for releasing his work into the public domain. However, it should be noted that our intention was not to recreate all of the functions of REMEMOrizer, for example, the Speculator emulation and Virtual Tape support are not be included, but some other unique features have been added.

A Perfect Storm

Design Goals

• CP/M Disk system based on SD card

• RAM Expansion up to 512kB (starting from 0k, 32k/MTX500 and 64k/MTX512)

• VGA Output for CP/M (80 columns) and VDP (40 columns & graphics)

• Network Connectivity based on the work done for NFX

• Utilizing a "low cost" FPGA development board

• Designed for internal mounting only

Other Design Goals & Limitations

One of the issues raised by users of CFX (and REMEMOrizer) is the way that externally mounted devices hang off the end of the MTX. The plan for MFX was that the board would primarily be designed to be mounted internally, with the required I/O connectors exposed for ease of connection, likely through the right hand end plate. However, external mounting was also considered.

Since MFX boards are hand built, primarily by myself, one of the issues is that FPGAs are typically produced as surface mount components which do not lend themselves to hand soldering - at least, not to someone with my soldering "skills". Therefore, in a similar manner as REMEMOrizer, the FPGA is incorporated using a low cost development board with pin header connections to a parent PCB.

I did a little "Googling" and came across a minimum system development board based on the Altera Cyclone II FPGA. When I suggested it to Martin, it turned out that he already had one! Grant Searle had used the board a few years ago as the basis of his Multicomp project - creating a number of different micros using the same FPGA development board, and Martin had implemented it himself.

As noted above, Andy's first reimagining of the MTX was REMEMOTECH, created on an Altera DE1 board, which also used a Cyclone II FPGA, so there was lots of scope for plagiarizing Andy's code :-)

Similarly, the SD card and any other modules that use SMT components are incorporated using prebuilt daughter boards.

This inevitably meant that the MFX board needed to be considerably larger than CFX or REMEMOrizer and likely to be around the size of a Eurocard PCB. The MTX case is conveniently sized such that a 160mm long PCB matches the PCB guide slots perfectly. It was envisaged that a 3D printed replacement endplate for the MTX will be used to expose the I/O connectors. Depending on the final board design, the I/O connectors on the board were intended to either be connected by flying leads or the board wouldbe made wide enough that the connectors could be directly mounted to the PCB and the endplate.

The MTX expansion boards that we have produced to date have used edge connectors that are relatively easily available. These connectors are intended for mounting at a right angle to the board, rather than the straight edge connectors used by Memotech's expansion cards. This has the effect that the PCBs is not level with the MTX motherboard and, when mounted internally, the PCBs do not align with the PCB guides. For MFX, it was necessary to use harder to source (and more expensive) straight connectors.

Update : May 2022

As development has progressed and we have confirmed its viability, we can now reveal the "mystery enhancement" mentioned on an earlier version of this page. Although, for anyone familiar with Martin and I's projects to date, it is probably not a great surprise that the "mystery" is network connectivity based on the work done for NFX.

Whilst this connectivity will allow the MTX to run a basic webserver, to my mind, the greatest benefit for users will be the ability for the user to transfer files to and from MFX using FTP. Given the inherent limitations of a 4MHz Z80 CPU, it will not be particularly fast, but it should be much more user friendly than the existing methods for transferring files between the MTX and a PC.

Update 2 : May 2022

Development of the technical aspects of MFX have progressed well, to the point where we are now confident that a "product" will be released in due course. I have dropped the "maybe never" comment on MFX's availability and put a more definite target date of "Late 3Q 2022" on it.

Martin has more or less completed design and testing of the basic functionality of MFX but software development will continue. 

On a slightly negative note, we had hoped that the MTX would be capable of powering MFX without the need for an additional external power supply (that was possible with Memotech's internal 80 column expansion board), however, whilst the video output from Martin's prototype board was perfect when using an external PSU for the FPGA board, some "ripple" was seen on the VDP AV output when taking power only from the MTX's 5V power rail. It is possible that this is specific to Martin's MTX and/or PSU, but it is safer to assume that an external 5v, "wall wart" will need to be part of the MFX deliverables.

The hardware design is complete to the point where the PCB electrical design can be completed. However, further work is required on the physical layout of the board to finalise how the I/O (VGA monitor, SD Card and network) interfaces will be connected. Once this phase is complete, I intend to order up a small batch of boards, mainly to confirm that I have the design right before I commit to a larger run of PCBs - assuming of course, that anyone is interested  in purchasing MFX?

Update 3 : June 2022

Design of the PCB is close to completion. I have made a change to the board's footprint - it is now quite a bit wider and the same size as Memotech's internal SDX 80 column card, i.e., it will now take up the full width of the case between the MTX computer board and the right hand end plate. This will slightly increase the cost of the PCB but should save on the total cost as all of the I/O connectors will be available at the end plate - internal patch cables will not be required.

I was in two minds whether to use full size or Micro (TF) SD card modules and in the end decided to hedge my bets and design the PCB to support both sizes - though only one at a particular time. It will be possible to change the module used after construction but the end plate will likely have to be different.

There are pros and cons with both card sizes, TF cards seem to be slightly cheaper, but they can be quite fiddly to use, particularly for, in Martin's words, "fat aging fingers ". Of course, SD to Micro SD adapters could be used, and some people may prefer to use TF cards anyway. The choice of SD card size is likely to be a user option - possibly the best solution all round.

Update 4 : July 2022

A test batch of PCBs has been fabricated and, despite some minor issues which will be tidied up on the next production run, the boards work well and have demonstrated that MFX is going to be a reality. Some minor modifications to the firmware were necessary to resolve a couple of minor issues that appeared when the firmware was loaded onto the PCBs, rather then Martin's wired prototype board, but the design is now essentially complete. The plan is that we'll spend another couple of weeks testing to ensure that no hidden gremlins appear, then I will make MFX available for purchase, probably by the end of the month.

I have made a fair sized investment already, including a bulk buy of connectors and gathering together other modules and components, so I'd like to recover some of these costs before I spend too much more. To that end, I will assemble the few remaining PCBs that I have here and, assuming that anyone actually wants to buy them, I will use the proceeds of these sales to get a larger quantity of PCBs fabricated and purchase additional modules and components so that MFX can be made more widely available.

I had hoped that, by now, the global supply issues that we've seen over the past couple of years would have started to reduce; unfortunately though, there seems to be little sign of that happening in the near future. In fact, in the UK at least, things appear to be getting worse! The rapidly rising rate of inflation, coupled with the decline of sterling against the US dollar means that prices are going up, rather than down. In particular, the "low cost" development board is no longer that! I will be fixing the initial price for MFX in the next couple of weeks, though the price is likely to be pretty fluid, at least for the next few months.

Update 5 : 21 July 2022

"Final" testing with the initial run of PCBs identified an intermittent problem with transferring data from the WIZnet module. Martin was able to figure out the cause and made design change to fix it. Unfortunately, the fix means that a minor wiring change is needed to the PCB. On the PCBs that Martin and I have assembled, we have installed a couple of patch wires to connect the WIZnet R/W signals to the FPGA so that these signals could be "de-glitched". Whilst the modified PCB's work fine, I have decided not to assemble the rest of the PCBs from the initial manufacturing run and will order up a new batch of V1.1 PCBs - this will mean a couple of weeks delay before MFX becomes more widely available, though, baring any other unforeseen problems, it should still be around the end of this month.

As an aside, a note about trying to source items from some of the Chinese sellers on AliEpress and Amazon Marketplace . . .

Based on my trying to source some of the items that I need for MFX, mainly the FPGA module, it is clear that many of the "suppliers" advertising these parts do not actually have them available. You will often see prices quoted and availability indicated on the websites, but when placing an order, find that the "supplier" fails to deliver, often on the basis that "there was a problem with shipping", or "the item is no longer available", or some other, equally disingenuous remark. In reality, it appears that many of the "sellers" only attempt to obtain the items once they actually have an order and find that the wholesalers who actually do have stock have increased prices since the retailer may have checked the prices (assuming that they even did) many months or even years ago.

It has been my experience that the purchase protection offered by the market place sites works and I have not lost money, but the "sellers" don't bother to flag up any issues until after the delivery due date, or wait until you report a failed delivery, which is often WEEKS after ordering, so I have been out of pocket for quite a while until the refunds get processes. This is annoying, but the bigger issue is the lack of certainty on when I can obtain the parts.

The FPGA modules are still available, but in order to "guarantee" availability, it is likely that I am going to have to use some of the more expensive retailers who at least seem to be more willing and able to deliver.

Update 6 : 31 July 2022 - Final (hopefully!)

The updated PCBs have arrived and I will shortly start assembling devices in preparation for shipment. I have also ordered up a number of 3D printed end plates in a variety of materials to try and find one that does the job at reasonable cost with good quality. I will likely hold off shipping any boards until the chosen end-plate can be shipped at the same time. Apologies for the delay, but in view of these points, I will probably not be in a position to ship any MFXs until mid August.

As an aside, I checked Digikey's latest price for the edge connectors today and was somewhat shocked to find that they have more than doubled since my first order. I have enough in stock to fill the first orders and quite a few extras at the moment, but if MFX proves to be very popular (and I think it might), then I'll either have to try and source different connectors or the price will likely need to increase a little, but that will be quite a few months down the line.

You can read about the development of the design of MFX here.

M F X   A V A I L A B I L I T Y

Released Late 3Q 2022

Now shipping - in small numbers !