ISA CompactFlash

Best Ever ISA CompactFlash PCB


The Lo-tech ISA CompactFlash Board has been a consistent best seller since it’s launch back in 2013. Having been through a number of relatively minor revisions, I’m today pleased to announce availability of the best version yet!

Now formally rev.3 and made in the UK, the PCB features a thicker, 2.5µm gold card-edge connector for long-term durability as well as ENIG finish for easy soldering and bevelled edge.


The design also includes ROM address selection, PC/XT slot-8 functionality with disable jumper, and more durable power supply for key-pin powered DoM and CompactFlash adapters with an optional 2.2uF tantalum capacitor at the header.

The SMT components on the back of the board remain optional, meaning this design is still the cheapest, easiest to assemble, fastest, and most compatible storage adapter for PC and PC/XT class hardware.

The ISA CompactFlash PCB is available in the site store now.

Revised ISA CompactFlash PCB

This board should have been called the ISA CompactFlash Adapter rev.3, but somehow the design made it to fab with the development title rev.2b still intact… but anyway, here it is!


This revision of this ever popular project has two changes designed to make it even more compatible:

  • a selectable ROM address – either C800h or D800h – makes it possible for this adapter to co-exist with an MFM or RLL device, for example for data transfer (requires SMT resistor R4 to be fitted);
  • a jumper (JP3) to disable CARDSEL drive signal, making it possible for adapters with the SMT components fitted to be used in systems that cannot boot when this signal is present, such as the IBM PS/2 Model 30-286.

Full information in the wikiPCBs are available now!

Announcing… the XT-CF-lite rev.2

The XT-CF-lite board arose almost out of frustration with the reliability issues in the CPLD based XF-CFv2, but it was instant hit – it’s probably the most-cloned Lo-tech board, with various unbranded re-spins appearing on eBay throughout Europe and Sergey’s through-hole version in the USA.

Following on from that, announcing then the rev.2: XT-CF-lite-rev2-1536px

What’s Changed?

  • Data bus buffer to ensure signal integrity in heavily loaded ISA buses
  • Slightly cheaper component list (BoM)
  • Works in PC/XT Slot 8
  • Simpler configuration (two options for ROM Address and IO address via simple jumpers)

As always, full details and schematic are available on the site wiki.

ISA Slot Bracket

The pictured ISA slot bracket is 3D printed (SLA process) and includes guide rails and an exact Type II cutout, making it much easier to insert the card than with the previous punch-press bracket. The plastic is however fragile and though perfectly adequate once installed, it’s easy to break the tabs when fitting the card. 3D printing is however a rapidly evolving field and more prototypes, this time metal, are due towards the end of the month – watch this space!


Testing has been performed with this board in my ever-stable IBM Portable PC 5155. Besides the usual functional testing (flashing the BIOS and formatting media):

  • Copied 16,000 files (mixed of source and object code) totalling 1.2GB three times – on CompactFlash in slot 5 and again in slot 8, and on a Seagate ST1 Microdrive in slot 5. Files then binary-compared with no differences found.
  • Ran pattern tests totalling 128MB on CompactFlash and again on ST1 Microdrive, both in slot 5.

With over 1011 bits transferred, this card has already been tested to beyond the quoted soft error rate of the original ST-412.

Any CompactFlash card or Microdrive should work, however there are some more recent CompactFlash cards that appear to have dropped support for 8-bit transfer mode (despite this being a required feature in the specification). Cards I’ve tested include SanDisk’s Ultra II and Kingston 4GB, and Seagate ST1 Microdrives.


The performance of this card is identical to all other current Lo-tech XT-CF cards, it will do between 190 and 300KB/s in a PC/XT, depending on the mode and media capabilities – much faster than an MFM drive, which generally did more like 60 to 90KB/s. It can reach about 1MB/s in a 12MHz 286.


The XT-CF-lite rev.2 PCB is available now in the site store. This card will not be offered as a kit due to the difficulty in splitting and shipping SMT components – a full BoM is provided in the site wiki for easy ordering of components from Mouser.

ISA slot brackets can be printed either at home or through a 3D printing shop using the STL file available from the site wiki. Metal processes are now available – I’ll be posting a review of three options later this month!

ISA CompactFlash Adapter and SD Cards


The Lo-tech ISA CompactFlash kit makes it possible to boot a vintage PC from a CompactFlash card in a straight-forward through-hole soldering project by means of a cheap CompactFlash-to-IDE adapter (like this). Whilst there’s long been interest in a similar SD-Card storage option, CompactFlash has always been just so much easier since it was designed for the ISA bus and supports an 8-bit transfer mode natively.

The development process for the (forthcoming) Lo-tech 8-bit IDE Adapter meanwhile involves testing as many different drives as possible, and it was perplexing that an SD-Card-to-IDE adapter just wasn’t detected, given that all the real hard-drives so far tested worked OK. This got me thinking.


In hacking the XT-IDE Universal BIOS (XUB) to work with the new 8-bit IDE adapter, I’ve simply re-used the existing XT-CF ‘BIU’ controller type (designed for CompactFlash and so making use of the 8-bit transfer mode) and bypassed the error checking on the 8-bit mode set command. This allows the disk to stay in 16-bit transfer mode (because generally 8-bit transfer mode isn’t supported by real hard-disks) and leaves the magic to the hardware on the 8-bit IDE Adapter. This works OK, but… what if the SD-to-IDE adapter actually supported 8-bit transfer mode?

In that case, the BIOS would set 8-bit transfers, then only ever retrieve half the sector data interspersed with random garbage, since the logic on the new adapter would be storing the high 8-bits which we’d just configured the device not to present. So could the SD-to-IDE adapter work on the ISA CompactFlash adapter?


Lo-tech ISA CompactFlash Adapter booting from an SD card interfaced via an FC1306T based adapter

FC1306T (GP)

The SD-Card adapter I was testing was based on the FC1306T chip, and the answer is right there in the datasheet: it’s actually an SD-to-CompactFlash adapter, “Fully compatible with CFA (Compact Flash Association) Standard”, which of course includes 8-bit transfer mode.

FC1306T based adapters seem to be in plentiful supply – in header, cable or slot-mount types, and any adapter based on this chip should work!



FC1306T based SD-Card to IDE adapters support 8-bit transfer mode

Performance wise these run at about the same speed as a basic CompactFlash card – around 200KB/s in an otherwise stock PC/XT. The slot-mount type need some care in mounting as they have PCI profile brackets, with the card mounted on the other side. I found it could be bent a little for use in an IBM Portable PC 5155 slot 8, providing externally accessible SD card storage and using a slot of otherwise limited use.


SD card throughput in an otherwise stock IBM Portable PC 5155

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