IBM XT ALPS Drive

[Mike_Z]

Seems there must be a black cloud over my floppy drives these past few weeks. First I had trouble with the 5 1/4 Shugart drive on my SOL-20, then one of the Shugart 8 inch drives on my CP/M machine failed. This morning the A: drive on my IBM XT failed. So I opened it up and found that I have two ALPS DFC222B02A floppies. The A: drive doesn't seem to be seeking properly, maybe one of the stepper drive transistors is bad. BUT... I don't have any information or schematics for these drives. I looked around on the internet but didn't find much. Does anyone have any suggestions or pointers to such documentation? Thanks, Mike

[Mike_Z]

Well.... that was easy. I tried a set 1.2 Mb drives and they worked fine. Then I inspected the ALPS. Re seated the plugs, terminators and the cards, then just like that it started to work again. Been testing the drive for an 1/2 hour or so and it still is working. So maybe I was given a present early. Yet, I still don't have any information regarding these ALPS drives and I may someday really need them. I looked at Bit Savers and there is just a patent document. Mike

[Mike_Z]

One item that seems a little odd, both drives are strapped as DS1. I tried changing the A: drive to DS0 and it would not work. Apparently, the DS is changed in the ribbon cable. Mike

[hornbetw]

IBM & compatibles strap the drives as DS1. The twist in the drive cable swaps the Drive Select so you can plug the drive in any position and have it work without changing the jumpers on the drive. The Tandy 1000 series and some other compatibles don't use the cable twist, so you have to change the jumper to select the proper drive position.

Tom

[modem7]

IBM & compatibles strap the drives as DS1.

The second drive-select position:
DS2 if the the drive's jumpers are {DS1}{DS2}{DS3}{DS4}.
DS1 if the the drive's jumpers are {DS0}{DS1}{DS2}{DS3}.

The twist in the drive cable swaps the Drive Select ...

And per the diagram at [here], the motor-on lines as well.

The Tandy 1000 series and some other compatibles don't use the cable twist, so you have to change the jumper to select the proper drive position.

And some of those requiring that the drive be configured to turn the spindle whenever the drive is selected (i.e. ignoring the motor-on line).

[Chuck(G)]

The IBM scheme gave up the ability to run 4 drives off the same cable in exchange for being able to control the spindle motors of either drive independently.

On a "straight through" cable setup, where drives are addressed by different DS settings, all spindle motors operate at the same time. Given the low capacity of the 5150 power supply (63.5W), conserving power was important.

There are a couple of third-party controllers that allow for operation of a third drive on a "twisted" cable by using extra unused conductors in the cable (e.g. many DTC hard/floppy controllers), but the twist for the third drive is a bit bizarre. Actually, any controller using the National DP8473 can be rigged up this way with just a patch wire or two on the controller PCB. I've configured a Future Domain ISA SCSI controller this way, for example.

[Mike_Z]

Seems each vendor has their won ideas as to how things should be done. This standard is followed by every vendor product I've come across. That is a good reason to find some documentation regarding the ALPS drives. I still have not found anything helpful, but my need for it is not immediate, I'll keep looking, thanks for the help, Mike