Lo-tech XT-CF Board

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Lo-tech XT-CF Board Assembled (first prototype)

The lo-tech XT-CF Board is a bootable 8-bit ISA card with a CompactFlash header mounted so that the CF card is accessible through a custom ISA expansion slot bracket. This card has been designed for use in IBM PC/XT, PC/AT and all compatible systems.

Note: the current iteration of this card is the XT-CFv3.

Key Features:

  • Replace dead MFM or RLL hard disks (and their controllers) with a cheap CompactFlash or microdrive media
  • Easy to access CompactFlash card without opening the PC
  • Reduce system power consumption (and hence load on the PSU) by as much as 30W
  • Uses the XT-IDE Universal BIOS (adapter type 'lo-tech XT-CF')
  • Increase system performance - offers 5x the throughput of an ST-412
  • 32K in-system re-programmable ROM (24K free for any other ROM code)

The board is derived from the Dangerous Prototypes V2 board, and uses the same Xilinx XC9572XL CPLD.



  • 8-bit ISA card with header for type-I or type-II CompactFlash media
  • CompactFlash header configured to operate media in true-IDE mode
  • 500mA 3.3V regulator can drive microdrive or CompactFlash cards without any external power connection (330mA power budget for microdrives)
  • Line driver for on-card and external activity LEDs (30mA power budget for external LED)
  • Low-cost SMT Flash memory chip with 32K usable
  • JTAG header for CPLD programming

Modes of Operation

  • 8-bit Port-mapped IO
  • 16-but Port-mapped IO (supported on most systems; provides a performance advantage with 8088 and 8086 CPUs)

Operating mode is configured in the BIOS and can be switched on-the-fly between modes using the lo-tech XT-CF Configuration Utility. The board is functionality identical to the XT-CF-lite, and with one jumper-wire fitted can also implement ISA B8 line functionality of the XT-CFv2, allowing use in IBM Personal Computer XT System Board Slot 8.


Lo-tech XT-CF Board

Boardhouse Requirements

  • 8 mils clearances and minimum track width
  • 0.4mm minimum hole size
  • Can be manufactured on a 100x100mm board
  • Gold fingers are preferable but not required

Assembly Notes

  • Thoroughly wash the PCB before assembly with Isopropynol
  • Place the CF socket, CPLD and flash chip first
  • Next place the VRM, LED driver and resistor networks
  • Then place LEDs, resistors and SMT capacitors
  • Next thoroughly wash the board using a toothbrush to ensure flux is removed from between SMT pins
  • Next add the through-hole components (DIP switch, headers and 47uF capacitor), then wash again
  • Before use inspect all connections with a magnifying glass to ensure there are no shorts between pins. Inspect the CF header leads as solder can sometimes flow up the leads during assembly causing a short away from the PCB itself.

Bill Of Materials

Farnell Parts List:

Part(s) Description Package Value Qty Required Farnell Code
IC1 XC9572 72-cell 3.3v CPLD TQFP100 - 1 1193233
IC2 SST39SF0x0A Flash TSOP32 (8x14mm) 1, 2 or 4Mb 1 1829977
IC3 SCHMITT TRIG, INV GATE 74LVC1G14 SOT-25 - 1 1893833
VR1 SPX3819M5-L-3-3 - LDO, 500MA, 3.3V, LOW NOISE SOT-23-5 - 1 1831949
C1 Low-ESR Electrolytic Capacitor Radial, 5mm pitch, 10mm max diameter 47uF to 100uF, 10V+ 1 1692338 (future: SMD 1850100)
C2, C14 Ceramic Capacitor (X5R or X7R) 0805 10uF, 10V+ 2 1833812
C12..13 Ceramic Capacitor (X5R or X7R) 0603 1uF, 10V+ 2 1828801
C3..11 Ceramic Capacitor (X5R or X7R) 0603 0.1uF, 10V+ 9 1414610
R1..2 Resistor 0603 RESISTOR, 10K, 0.1W 2 1469748
R3, R5 Resistor 0603 RESISTOR, 1K, 0.1W 2 2008355 or 1652848
R4 Resistor 0603 RESISTOR, 270R, 0.1W 1 2059585
R6 Resistor 0603 RESISTOR, 5K6, 0.1W 1 1739171
RN1, RN2 Resistor Network 1206 RESISTOR NETWORK, 10K, ± 2% 2 1770137
LED1 Low-current LED 0805 LED, SMD 1 1685055
DIP_SW 9-way DIP switch DIL SWITCH, DIL, 9WAY 1 1255227
CF1 3M N7E50-Q516 Compact Flash Header - 3M N7E50-Q516xx-x0 1 1267444
EXT.LED 2-pin Header - HEADER, 1ROW, 2WAY 1 3418285
JP1 3-pin Header - HEADER, 1ROW, 3WAY 1 3418297
JTAG 6-pin Header - HEADER, 2ROW, 6WAY 1 3418492
- Jumper for CF Card Voltage Selection - - 1 1740370


  • EXT.LED and R4 can be omited if external activity LED is not required
  • LED and R5 can be omited if on-board activity LED is not required
  • IC3, R4, R5, LED and EXT.LED can be omited if no activity LEDs are required

ISA Bracket

XT-CF Adapter ISA Bracket
  • ISA Bracket Design per sketch
  • To minimise production cost, design has no threaded holes (simple nut-and-bolt required)

CPLD Logic


Programming the CPLD

See lo-tech XT-CF CPLD Programming Guide.



  • Board design permits the use of SST39SF0x0A flash chips (TSOP32, 8x14mm) of 1Mb, 2Mb or 4Mb capacity
  • Regardless of the chip used, the first 32KB only will be mapped into the PC address space
  • Base address configuration per DIP Switch Settings


Compatibility and Interoperability

Use with Other Cards

  • The IO port address set via the DIP switches must match that set in the XTIDE Universal BIOS configuration utility
  • The BIOS address can be changed via the DIP switches without changing the BIOS itself


  • All CompactFlash media can be used. Media supporting multi-sector transfers will provide a performance advantage.
  • The adapter can be used in any system supporting 8-bit ISA
  • 8-bit Port-mapped IO transfer mode is slowest but most compatible
  • 16-bit Port-mapped IO (BIU offload mode) is not supported on some early PC/XT clones, due to system logic errors
  • ROM shadowing will offer significant performance gains on newer hardware, since the flash ROM is 8-bit so BIOS instructions can be fetched much more efficiently from system RAM

DIP Switch Settings

Switch Function On Off
1 ROM Enable Enabled Disabled
2 ROM Base Address C800h D000h
3 IO Port Address 300h 320h
4** ISA B8 Enable Enabled Disabled
5** ISA B8 Function Type (if enabled) PC-AT (Zero-wait-state) PC-XT Slot 8
6* Not used - -
7* ISA B8 Output** - -
8* Not used - -
9 ROM Write Enable Enabled Disabled (ROM cannot be written)

*Switches 6-8 must be OFF. Switch 9 can be left ON, since the flash chip includes Software Data Protection that prevents accidental corruption or overwriting.

**To use the ISA B8 function, wire a jumper from Sw7 resistor-side to ISA B8 pad (see photo).

Default settings: ROM enabled, IO port 300h, ROM base C800h:

1 2 3 4 5 6 7 8 9

Note that the IO base address is set within the XTIDE Universal BIOS ROM image via the Universal BIOS Configuration and Flashing utility. The IO address set within that utility must much that configured on the card. Should the IO port address be changed for any reason, the BIOS must be updated and re-flashed to the XT-CF card (using the lo-tech XT-CF flash utility).

The BIOS address is determined at boot time by the XTIDE Universal BIOS. Since the code has been designed to be relocatable, the BIOS base address can be changed without the need to reconfigure the Universal BIOS.

Known Issues

  • Activity LED is lit when a CF card isn't inserted. Could be resolved by adding a 50k PU to /PDIAG.
  • 47uF through-hole capacitor holes are placed too wide (spaced for ~100V capacitors).
  • Switch numbers are reversed in the schematic
  • ISA B8 isn't connected, hence card cannot be used in slot 8 of IBM PC/XT (see note above)

See Also