Clock profile switcher for timing-sensitive software and test harnesses, enabling controlled transitions between true legacy rates and turbo operation.

Profiles

4.77MHz, 8MHz, 12MHz, board turbo

Switching Logic

Debounced hardware line with deterministic latch state

Feedback

Status LED map plus software verification hooks

Compatibility

AT clones, 386SX, selected 486DX boards

Use Cases

Cycle-sensitive DOS software and diagnostics harnesses

Field Harness

Front-panel and relay control compatible

The Lo-tech ISA CompactFlash Adapter is an open-source 8-bit ISA card that enables modern CompactFlash storage on IBM PC XT, AT, and compatible systems. Paired with the XTIDE Universal BIOS, it provides silent, reliable mass storage for vintage computers using inexpensive CF cards. The design uses only five through-hole ICs, making it accessible for home assembly. Originally designed by James Pearce at Lo-tech, with hardware schematics and BIOS source code freely available.

Bus Interface

8-bit ISA (fits any PC/XT/AT 8-bit slot)

Storage Media

CompactFlash Type I/II via 40-pin IDE header

I/O Address Range

300h–31Fh (300h–30Fh active)

ROM Address

C800h (32 KB window, directly flashable in-system)

Flash ROM

SST39SF010A 128KB (32 KB used) — in-system programmable

Compatible Flash ICs

SST39SF010A, SST39SF020A, SST39SF040, AMIC A29010

Supply Voltage

5V from ISA bus

IC Count

5 through-hole DIP ICs (basic build)

PCB

2-layer, ISA form factor, through-hole only

BIOS

XTIDE Universal BIOS — GPLv2, supports up to 4 IDE controllers

Transfer Modes

PIO-8 (standard), PIO-8 BIU Offload, PIO-16 BIU Offload

Max Drive Capacity

Unlimited with MS-DOS 7.x/FreeDOS; 8.4 GB limit on DOS 3–6