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Possible to hack the SCSI ID on external Zip drives?

O

Old Thrashbarg

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I recently picked up a couple external SCSI Zip drives, with the idea of using them as boot drives for some of my old machines. Unfortunately, there's a troublesome little detail that I'd forgotten about these drives... they only have two settings, ID5 or ID6. For use as a regular external storage drive that's fine, but it presents a problem if I want to boot from them, as a fair number of old SCSI controllers expect the boot drive to be at ID0.

So I've been trying to figure out a way to modify the things to use a different ID. At first I thought it would be a simple matter of cutting a couple traces to get ID0/1. Judging by the way the jumpers work on most SCSI drives, I figured there would be three lines for the SCSI ID, one would be permanently tied to ground, and there would be a SPDT switch on the other two that would alternately ground them. But it appears that Iomega didn't make it that easy... there's only one line coming to an SPST switch, from the custom Iomega 'Phaedrus' chip, which is open for ID6 and grounded for ID5. And since there's no data available on that chip, I've kinda hit a wall. I suspect the key may be to look at one of the internal SCSI drives, but that would require having an internal SCSI Zip drive, and those things are quite difficult to find.

Now, there's no way I'm the first person to think of doing this, but has anyone ever actually done it, or am I wizzing in the wind here? I've Googled just about everything there is to Google on the subject, and I've come up empty. :(
 
Hmmm. The Phaedrus (made by a company of that name) is an 8052-based microcontroller. Short of making some sort of making an active adapter to change the SCSI ID, I suspect that the SCSI ID code is embedded in the chip firmware and that you're stuck.
 
I'd just get a better SCSI controller.

Nearly any Adaptec with a BIOS can boot from an arbitrary SCSI ID. I had bootable Win95 and DOS 6 running from a SCSI Zip using one.


Mike
 
That solution only works when you can get a better SCSI controller. I primarily wanted to use the Zip with my PC6300. I have a TMC-850 in it, which is already pretty much the best of the limited options for 8-bit SCSI cards, and I've never been able to convince it to boot from anything other than ID0.

It's not like I don't have other options, it's just that none of the other options are quite as attractive. Zip drives are small, quiet, easy to move around between different machines, and I already have a few dozen disks for 'em. If I want to play around with different OSes or whatnot, all I'd have to do is swap out the disk, and likewise, if I want to transfer stuff to/from my main PC, all I'd have to do is pop the disk into the drive in my main PC.

But if the ID setting is an issue with embedded microcontroller firmware, then that's more trouble than I want to get into. I guess the Zip drives will just have to be relegated to Amiga and Mac duty and I'll come up with something else for the 6300.
 
Old Thrashbarg said:
That solution only works when you can get a better SCSI controller. I primarily wanted to use the Zip with my PC6300. I have a TMC-850 in it, which is already pretty much the best of the limited options for 8-bit SCSI cards, and I've never been able to convince it to boot from anything other than ID0.

It's not like I don't have other options, it's just that none of the other options are quite as attractive. Zip drives are small, quiet, easy to move around between different machines, and I already have a few dozen disks for 'em. If I want to play around with different OSes or whatnot, all I'd have to do is swap out the disk, and likewise, if I want to transfer stuff to/from my main PC, all I'd have to do is pop the disk into the drive in my main PC.

But if the ID setting is an issue with embedded microcontroller firmware, then that's more trouble than I want to get into. I guess the Zip drives will just have to be relegated to Amiga and Mac duty and I'll come up with something else for the 6300.
Click to expand...

I'm with you - I like the SCSI Zip a lot too.

Another option is to just use it as is - boot from a floppy with the removable storage ASPI drives and use it as a logical hard drive. It won't have BIOS support as a hard drive, but at the DOS level it will look and smell like a hard drive. I used a parallel port attached SCSI drive for years like this on my PCjr. For backups I just had to move the drive to a Linux box.


Mike
 
It may be second nature to you, but hacking around in assembly is a bit outside of my abilities.

I'd eventually like to learn such things, but at this point in time, that'd be far more effort than I feel like putting in just to be able to use a Zip drive...
 
If you don't want to hack the ROM, how about constructing a translator circuit? You know, one that sits between the Zip drive and controller, translating target ID 0 (or whatever you want) commands / data to target ID 5 or ID 6.
Maybe not easier, but a challenge noen the less. :)
 
tingo said:
If you don't want to hack the ROM, how about constructing a translator circuit? You know, one that sits between the Zip drive and controller, translating target ID 0 (or whatever you want) commands / data to target ID 5 or ID 6.
Maybe not easier, but a challenge noen the less. :)
Click to expand...

That's what I suggested at #2 above, but it wouldn't be simple--you'd have to make a pass-through device, since the SCSI ID is presented on the same lines that carry data. While it might make a nice project when you're snowed in, it'd be easier hack the controller BIOS.
 
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