Solidisk DDFS & DFDC

Solidisk DDFS issue 1 (introduced mid 1984)

A 1770 diskinterface that's not compatible with Acorn's late 1985 DDFS and therefore not with Acorn's ADFS chip. There are ADFS ROMs for this disk interface from Solidisk itself though. All the DDFS's up to the release of Acorn's 1770 disk interface kit for the BBC B, used their own addresses for the disk interface, most of which were 1770 based (some on the 1797 and other Western digital disk controllers).

Solidisk DFDC issue 1 (introduced late 1984?)

This is a switchable diskinterface for 1770/8271, but the 8271 need not be installed. Same as the DDFS, this version is not compatible with Acorn's 1770 disk interface kit. I could not get this to work with dual drives at first; when accessing drive 2, drive 1 was also accessed giving a disk fault. The problem is that pin 2 of the 8271 socket is not connected (which goes high and drive 0 is ALWAYS selected (see the BBC circuit diagram)). I solved this as follows to see if that was all:

I used a 74LS00 as an inverter:
 - pin 6 of connector that goes in the 8271 socket on the BBC PCB
(=drive sel 1) -> invert -> pin 2 (=drive sel 0).

This gives a mess of wires but now both drives work!

UPDATE: I finally got hold of the Solidisk DFDC installation instructions, and for this, the IC 79 with soldered wire from pin 4 to pin 11 also needs fitting (as on the standard Solidisk DDFS). Why didn't Solidisk just invert the FD0 select signal on the DFDC board?

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