PCjr (Was Re: IBM PC hacking)

[Tony Duell]

> > IIRC, the TechRef for the 10MByte controller contains a schematic with
> 3 
> > chips simply labelled LSI A, LSI B and LSI C. It was fairly obvious
> from 
> > the piuout that one of this was nothing other than a Z80 processor. I 
> > think one of the others was something standard too.
> > 
> Is that the Xebec controller?  (can't remember if that's who IBM got the

I beleive it is a Xebec.

I also have found the same custom hard disk controller chip (the chip
that's not the Z80 or the other standard one) on one of the SASI-ST506
Xebec bridgeboards. In fact I repaired such a bridgeboard with a chip
taken from an old XT hard disk controller (flame me if you like, the
machine the bridgeboard went in was more interesting to me than an IBM
PC/XT). 

I've never tried a Z80 chip on the IBM PC/XT hard disk controller card, 
so it's possible there's something odd about it. But actually I doubt 
Xebec would have got a custom-microcoded Z80 processor made for that 
board, or anything like that (IBM probably _could_ have done. but it's 
not AFAIK an IBM design). Certainly if that chip failed on one of my XT 
controllers I'd fit a Z80A and see what happened.

-tony