CompuServe Drives: Custom firmware?

Tothwolf tothwolf at
Sat Apr 18 02:48:35 CDT 2015

On Sat, 18 Apr 2015, Cory Smelosky wrote:
>> On Apr 18, 2015, at 02:55, Eric Smith <spacewar at> wrote:
>> My memory is probably faulty about exactly what the WD suffix means. I 
>> still think it's 16-bit "ultra" (1), but Wikipedia says that ultra (1) 
>> is single-ended or HVD, ultra 2 is LVD or HVD, and ultra 3, 320, and 
>> 640 are LVD only.
> The manual did confirm WD is definitely HVD which explains my issues.
> I recall some sort of Ultra bit in it as well.

I was writing this when you sent the above reply ;)

> ST34573WD
> ST32550ND

W -- wide
N -- narrow
WD -- wide differential
ND -- narrow differential

You'll need a converter. These type of differential drives can't be 
connected directly to a single ended bus, wide or narrow. If you do, you 
are connecting one side of the differential pair to ground, and these 
drives don't like that. There are also signal differences, see the pinouts 
for wide and wide differential and look at the pin numbers for attention, 
busy, ack, reset, etc. Later LVD devices could detect which sort of bus 
they were connected to, but these drives can't.

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