[sebhc] HDOS & IDE (was: H-8 question from a new list member)

[Lee Hart]

West, Ronald S. wrote:
> Thanks to all for the great ideas. I didn't know that the H67 was
> SCSI-like in its design. I have the H37/H67 board...

Aha! Then you have 90% of a hard disk implementation already done!

At the time the H67 was designed, it was called SASI (Shugart Associates
System Interface). It was later renamed SCSI (Small Computer System
Interface), but it is basically the same thing.

SCSI standardized on a 50-pin connector. At the time Heath did it there
was no standard, and they chose a 40-pin connector. As I recall, there
are just a few wires that are different. You can make an adapter with a
length of ribbon cable, a 40-pin, and a 50-pin insulation-displacement
connector. You slit the cable, and shift something like the last 6 wires
in 10 positions. 

The SASI/SCSI interface does not operate at the track/sector/cylinder
level. Basically, a hard disk just has "N" blocks of data. The actual
sector size and mapping between tracks/sectors/heads is all left up to
the drive itself. The drive does all the buffering and formatting.

> Will also review the drivers for the H67 as that will answer a few
> questions. Like, what sector size did they use & what disk size
> will HDOS 2.0 accommodate.

Again from memory, I don't think Heath supplied source for their
PREP/PART utilities, and they were written to assume a single 10meg
drive -- period. Other Heath aftermarket suppliers (Sigmasoft, Quikdata,
etc.) reverse-engineered them or wrote their own for other sizes.
Perhaps someone who had one of these setups knows...

> If someone has used a 128k SRAM chip (I think that was Eric)...

I used a Hitachi HM628512LP-70, which is a 512k byte part from Jameco
for about $20 each. Kind of expensive, but easy to use; it's a standard
32-pin DIP with generic bytewide-pinouts, not one of the tiny
surface-mount parts. The 128k byte equivalent is the Hitachi
HM628128LP-85, also from Jameco for $8.49 each.

> Also, does anyone know if the edge connectors are still available?

Do you mean the H8 and H89 Molex pin headers used on all the cards? Yes,
they are still a standard part stocked by any Molex distributor.

> Was wondering about how to modify the ROM code to allow booting
> from the eventual IDE interface but there may be a way to have
> the H67 boot code detect the new interface and use it instead
> of the H67.

If you use a SASI/SCSI hard drive, the existing code for booting from an
H67 should basically work. The main difficulties would be if you use a
larger drive and have more/larger partitions.
-- 
"Never doubt that a small group of committed people can change the
world. Indeed, it's the only thing that ever has!" -- Margaret Meade
--
Lee A. Hart  814 8th Ave N  Sartell MN 56377  leeahart_at_earthlink.net

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