SC504, v1.0, User Guide

SC504 is a Compact Flash interface designed for Z50Bus.

This card provides an 8-bit IDE interface via a 40-pin male header. In theory, you could connect other IDE devices, not just the recommended Compact Flash adapter module (shown above).

As this is a very simple interface, which uses the processor bus directly, without buffering, the IDE interface should not be extended for than a few inches and only carefully selected devices should be connected. In general, it is best to only use this interface to connect a Compact Flash card.

It is recommended that this card be placed close to the CPU card.

Not all Compact Flash cards are compatible with this simple 8-IDE interface. Older cards tend to be best. Large capacity, more modern cards are designed for very fast operation. This means very sharp edges on signals generated by the Compact Flash card. These edges can cause reliability problems with this simple, bus based interface.


The I/O address of this card can be set with jumper, JP1. The card occupies 8 I/O address, thus address bits 0 to 2 are not included in the address decoding.

Most new software will assume the I/O address for this card is 0x90 (binary 10010000). The other likely address is 0x10 (binary 00010000).

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Jumper positions for I/O base address 0x90
Jumper position for I/O base address 0x10


The device plugged into P2 (20 pin, 8-bit IDE) can be either self-powered or it can take power from SC504. The recommended Compact Flash adapter module must be powered from SC504.

As it is very likely the connected device will need to be powered from SC504, JP2 has a track connecting its two pads. Thus the jumper header and jumper shunt are optional. If fitted, the track between the pads of JP2 must be cut. This track is on the solder side of the PCB.


If the system is running RomWBW (which includes CP/M) the Compact Flash can be initialised for use with the CLRDIR command. CP/M does not need to be installed on the Compact Flash card as RomWBW is a ROM based operating system that includes CP/M.

If the system is running plain CP/M (not RomWBW) the Compact Flash card needs to be prepared before use. Instructions to install CP/M 2.2 on to a Compact Flash card can be found here.

The version of CP/M for this card, together with a Z80 processor card, is detailed here.

If you are using the Small Computer Monitor firmware then CP/M can be loaded and started from a suitably prepared Compact Flash card with the command “CPM”.

Homebrew 8-bit retro computing