Date   : Fri, 27 Mar 1992 21:37:41 GMT
From   : mtxinu!sybase!gaia!gng@ucbvax.Berkeley.EDU (George George)
Subject: Re: Info on NorthStar

There is absolutely nothing to prevent you from plugging a standard
S-100 disk controller into a NorthStar. You have to write a BIOS
which recognizes both the NorthStar & S-100 disk controllers. Yup,
you heard right - two disk controllers in one box. I know somebody
who did just that.

A few caveats.

IMHO the Horizion is more S-100 compatible than you think. :-)
I've had no trouble with mine. However, some of the signals are on
non-standard pins. For example, I had to move the refresh signal on
my SDS D-Ram boards, plus another signal (XRDY or PSYNC, I think).

NorthStar RAM is dynamic, and refreshing is done in a bizzare fashion.
DMA disk controllers (I think) won't work. You must use a wait state
based controller. I'm doing this from memory, so take a good look at
the schematics.

The NorthStar ridiculously puts its boot PROM at E800. Make sure that
memory stays free. You can put stuff above it, say at F000, but don't
stomp on the boot PROM. It is on the NS Disk controller and takes
about 256 (or 512, I forget which) bytes.

This weirdness limits you to a 58K CP/M. Your re-written BIOS may cut
that down a little further. I suggest moving the BIOS into the EPROM
socket on the CPU card and putting above your CP/M at F000.

All in all, an excellent S-100 beast.  My sincere Thanks to Curt Mayer.

... gng