Memotech Multi-Function Expansion System

MFX Support

MTX MFX Boot Screen

SD Card Directory

SD Card Compatibility

MFXs with serial numbers up to 18 were shipped with ROM versions that did not support partitioned media and were supplied with either a 512MB or 1GB micro SD card (of which 240MB or 754MB was wasted space). No problems were detected during testing and none have been reported since delivery.

Versions of the MFX ROM dated 14/01/2024 and later support SD cards partitioned partitioned in the PC sense, i.e., the CP/M "partitions" (disk images) and HEXTRAIN data file are saved to an area of the card with a Partition ID of 52 (CP/M). The remainder of the card can he configured as a FAT32 partition for use with a PC. Bill added this functionality and wrote a CP/M utility (fatcopy.com) that allows MFX to transfer files between the CP/M "disks" and the FAT partition. (This enhancement allows MFX to make optimum use of larger SD and SDHC cards, SDXC cards continue to be incompatible with MFX.) As small SD cards are becoming harder to find and more expensive, the majority of more recent shipments of MFX have been with larger, 4GB, cards.

The small number of SD cards that I have left over from the batches used for the initial shipments of MFX have been found to work well with partitioned media, but perhaps I just got lucky with the original supply.

Results with larger and more modern SD cards have been mixed. The situation is complicated by the fact that you cannot always tell exactly what flavour of card that you are buying when shopping on the likes of eBay and Amazon, cards advertised as being from a particular manufacturer are often fake!

When setting up new SD cards in this manner, I found that not all SD cards work well in this scenario and could exhibit a number of problems, such as not being bootable by MFX or having intermittent write problems. We have not been able to get to the bottom of why this might be, but it could be related to the access mode that MFX uses and the card's compatibility with it.

The SD specification advises that SD cards can be accessed in three modes, 1 bit SD mode, 4 bit SD mode and SPI mode. In order to use the SD modes in a design, a paid license is needed from the SD Association, SPI mode does not require a license, therefore, MFX uses SPI mode to access the SD card. It has been found that older cards support all of these modes, but newer cards may not support SPI or implement it in a non-standard manner and that older cards may perform better with MFX than newer ones.

If you experience problems with configuring a new SD card for MFX you might want to source a cheap, say Class 4 or Class 6, SD/SDHC card and try again. It seems that these issues are not unique to MFX, you can read about similar issues seen by Ralf Thelen (lisy.dev) on his page here. Martin and Bill have not seen many problems, but I have been buying quite a lot more cards from a number of different vendors and started to see more frequent issues with the cards that I was buying.

The failures that I have seen with a number of different SD cards are noted below, as with most things, YMMV!

Also note that one of my laptops provides more information when ejecting an SD card than others, usually giving the name of the manufacturer, or at least, the manufacturer's name that corresponds to the code that has been entered in the manufacturer field, which, in the case of many of the Chinese knock-offs, is not always accurate.

It is clear from the table below that finding suitable SD cards for use with MFX is not as easy as it should be. It is difficult to believe that so many of the cards that I have tried are failing to meet SD standards and I am starting to think that the SD code in MFX may have an inherent flaw that limits its use to a very small subset of SD/TF cards. This potential issue warrants further investigation, though this may not be easy as I was able to return most of the failing cards to the sellers for refunds. 

Description	Front	Back
Unbranded Generic 1 GB TF Card from AliExpress (purchased 06/22) The first batch of cards that I bough to ship with MFX with the early versions of the ROM. Came without adapters. Labeled as being from Taiwan.  R/W speeds somewhere between Class 6 and 10 Worked flawlessly and when tested with the later firmware, had no issues with partitioning or booting MFX. (Likely to be SD, rather than SDHC.)
Unbranded Generic 512MB TF Card from AliExpress (purchased 07/22) Again, bought to ship with the early versions of the ROM. Came without adapters and also labeled as being from Taiwan R/W speeds consistent with Class 6 Worked flawlessly and when tested with the later firmware, had no issues with partitioning or booting MFX. (Likely to be SD, rather than SDHC.)
"Kingston Canvas Select" - Not! Purchased from eBay UK, 01/24. When partitioned, fails to boot MFX. Identified as "Toshiba" under Windows 10 Capacity verified with h2testw but with slow W/R speeds, not Class 10 Advertised as "brand new and genuine Kingston from an authorized reseller." Poor quality packaging and printing, no unique serial number label. Confirmed by Kingston to be counterfeit. Kingston also advised that their SDHC cards have been discontinued and have not been manufactured by them for over 7 years.
"Mitos" Generic 4GB TF cards, available from many AliExpress sellers I bought a trial batch of 5 from AE and tested them with h2testw. The capacity verified OK and the R/W speeds were consistent with Class 10. I thought that they would be fine for MFX, but when I actually tried them some time later, I found that when partitioned, they would not boot MFX. Interestingly, they were identified as "Toshiba APPSD" under Windows 10. Even more interestingly, having wrongly assumed that these cards would be ideal for MFX, I purchased another 10 from the same seller. However, this time they worked flawlessly, although they had identical branding, they were identified as "Micron EITSD" under Windows 10. The cards were subtly different, the "bad" cards were marked "23K" and the "good" cards were marked "23L" (a later batch perhaps?). The good cards had what appeared to be a date code of 231209 (yymmdd?) on the reverse, but as they were ordered on 231213, that doesn't seem likely, though it's possible I guess (or the date code was yyddmm). The bad card had a code of 231028 on it, if it is a date, then being earlier than the 23L version does make sense. The most obvious difference is that the good cards were labeled "Taiwan" and the bad ones "China". I bought third batch of cards from a different seller which again were identified by Windows 10 as "Toshiba APPSD" marked "24C". I was pleasantly surprised when the card booted MFX, but writing was unreliable. These cards were labeled "Taiwan" but had a totally different set of printed text on the reverse, had no CE label (not that that means anything on many Chinese manufactured items) and did not perform as well as the "23L" version.
"Elite Pro" Full Size 4GB SD Cards (AliExpress) (purchased 02/24) Appeared to be reasonable quality and worked fine under Windows. When partitioned, fail to boot MFX.		(blank)
"Cloudisk" Full Size 4GB SD Cards (AliExpress) (purchased 04/24) Identified by Windows 10 as "Generic SD Card" When partitioned, boots MFX but HEXTRAIN data is unreadable
"Stickdrive" 4GB TF Cards (Aliexpress) (purchased 04/24) Identified by Windows 10 as "Micron EITSD" Works well when partitioned for MFX
"Silicon Power" 16GB SDHC TF Card (Amazon) Martin bought a couple of these off Amazon. Pretty nondescript branding, no issues with MFX, R/W speeds consistent with Class 10.		(blank)

Please let me know if you try other cards with MFX and how it works out for you and I will update the table accordingly.