uIEC/SD == AWESOME!

... except skiing through a revolving door :-) More seriously, there must be a limit to the code size. To goive you some idea as to the complexity, I think the HP Amigo drives had 8K of ROM, the SS/80 ones that I've worked on had 16K. This is 6809 machine code. The controller board contains a 6809, EPROM, RAM, the HPIB chip and standard-ish hard and/or floppy controller chips Obviously if you bit-banged it, it would take a little more code for that than to talk to the HPIB chips. I don't know how talking to a CF card (or whatever) compares to talking to a WD2973 floppy controller or a WD1010 hard disk contorller. But that should give you some idea. HPIB == GPIB == IEEE-488 (at least at the hardware level). Alas I don't think the standard -- IIEE-488-1975 is freely distributable (IMHO standards _should_ be, but they rarely are). I did read it once -- many years ago -- but I don't have it. If you can find it, it's somehting you should read. HPIB disk units tend to use many of the features of the HPIB standard. Early HPIB instruments tended to do the IEEE handshakes in hardware (either monostales, or state machines), so that's probably not a lot of use to you. The conputers tended to use 9914 interface chips, again not a lot of use. And HP's custom HPIB chip, the 1TL1 (Medusa) is nice, but not a lot of interest to you. Commodore almost always bit-banged it, so looking at the schematics of PETs and their peripherals might be a help. Otherwise just poke about on the Australian museum. Don't worry, it's 16 active signals : 8 data lines 3 handshake lines (DAV, NRFD, NDAC) 5 control lines (ATN, EOI, IFC, SRQ, REN) And then 7 logic grounds and a shield ground. All signals are bidirectional (although, unless you intend to be a controller, you don't ened to be able to drive some of them). Some devices drive them with totem-poll drivers, others open-collector (with passive termination). There are arguements in favour of either for particular applications. -tony