Lo-tech ISA CompactFlash Adapter

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Lo-tech ISA CompactFlash Adapter
Lo-tech ISA CompactFlash Adapter (back)

Note: This board has been superseded by the Lo-tech ISA CompactFlash Adapter revision 2

The Lo-tech ISA CompactFlash Adapter is a through-hole, small form factor 8-bit ISA adapter providing a 40-pin IDE header suitable for connection to a separate IDE to CompactFlash adapter. The design had several goals:

  • Ease of home assembly, by use of only through-hole components for basic operation
  • Small form-factor, to enable use in machines with limited expansion slot space such as the Tandy 1000HX, Sinclair PC200 and Amstrad PC-20
  • IBM Personal Computer XT System Board Slot 8 compatibility (with optional SMD components mounted on rear of PCB)
  • 5V supply to IDE header key-pin, for cable-less operation of CompactFlash adapters supporting this power option

The board is programatically identical to the XT-CF-lite and is therefore powered by the XT-IDE Universal BIOS, provided through an in-system re-programmable 32KB (addressible) flash-based ROM. Since the BIOS is only 8KB, 24KB is available for other purposes, and is byte-programmable. The board can therefore function as a universal ROM board, regardless of whether the IDE decoder logic is used (or indeed populated on the PCB).




  • 8-bit ISA card with 40-pin IDE header
  • 5V power supply:
    • to IDE header key-pin (can drive micro-drives or CompactFlash cards without any external power connection)
    • via 4-pin header (for direct soldered attachment of peripheral power cable)
  • Basic functionality is dependent only on through-hole components
  • Optional SMT components provide additional functionality:
  • Low-cost flash memory chip for boot ROM, with 32KB usable
  • Port-mapped IO; supports both 8- and 16-bit instructions (via partial address decoding)
  • Utilises XT-IDE Universal BIOS (adapter type: 'XT-CF')
  • Fixed resource allocation - IO ports 300-31Fh, ROM 32KB at C800h


Bill of Materials

Basic functionality requires only through-hole components:

Part Device Package Qty Farnell Mouser
IC1, IC3 74HCT688N DIP-20 2 382504 771-74HCT688N
IC2 AMIC - A29010-70F or SST39SF010 DIP-32 1 1896595 804-39SF010A7CPHE
IC4 74HCT139N DIP-16 1 382036 595-SN74HCT139N
IC5 74HCT245N DIP-20 1 382279 595-SN74HCT245N
R2, R3, R5 10k Resistor (3.5mm) - 3 9342419 270-10K-RC
R4 5k6 Resistor (3.5mm) - 1 9343369 270-5.6K-RC
C1..5 0.1uF Ceramic Capacitor C025-030X050 5 1100533 581-SR205E104MAR
C6 10uF Electrolytic Capacitor E2-5 1 8767084 647-UVR1C100MDD
HD1 T821140A1S100CEU 2x20 Pin Header, 2.54mm spacing 1 2215314 517-D2540-6002-AR
IC Socket - DIL32 1 1654375 571-1-390263-2
JP1, JP2, LED AMP - 826629-6 1x6 Pin Header (cut for each header) 1 3418327 571-826629-6

For IBM Personal Computer XT System Board Slot 8 compatibility and device activity LED, also populate these optional components:

Part Device Package Qty Farnell Mouser
U1 MC74ACT02DG SOIC-14 1 1607770 863-MC74ACT02DG
U2 SN74AHC1G125DBVT SOT-23 1 1105921 595-SN74AHC1G125DBVT
R1 RESISTOR, 0.125W 1% 130R - 1 9342567 270-130-RC
R6 RESISTOR, 10K, 125MW 0805 1 1612522 71-CRCW0805J-10K-E3
C7 CAPACITOR, 0.1UF, 50V 0805 1 2112751 581-ESD55C104K4T2A24
  • Board design permits the use of a range of DIP-32 flash chips (1, 2 or 4Mb):
  • Regardless of the chip used, 32KB is presented commencing C800h


  • JP1: ROM enable (closed = enabled)
  • JP2: Slot-8 function enable (closed = enabled)

An external LED can be attached to the 2-pin LED header only if the optional components (on the rear of the PCB) are populated. JP2 also depends on those components. Current limit for LED is 30mA.

The IO port address (300h - 31Fh) is fixed, as is the ROM address (32KB at C800h).

See Also