The Memotech MTX Series
Memotech Multi-Function Expansion System
Intended to be a development of the CFX
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
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 . . . .
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
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
In the current
global economic environment, designing new hardware and
sourcing the required components and modules is very
difficult; the cost and availability of parts that were
previously cheap and plentiful have both taken significant
backward steps, and, as of 1Q 2022, the situation showed
little sign of improving. This means that the price of the final product
needs to be
significantly more expensive than CFX/CFX-II - the target
price was around £100-£120, but that has proved to be
unachievable in the current climate, the price can hopefully be reduced as
global economics improve.
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)
Connectivity based on the work done for
Utilizing a "low cost" FPGA development
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
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
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
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
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
M F X A V A I L A B I L I T Y
Released Late 3Q 2022
Now shipping - in small numbers !