Daisy Chain 2 MFM Hard Drives

[Rizon]

I'm trying to daisy chain a Seagate ST-238R (MFM formatted) and an ST-225 on a Western Digital WDXT-GEN controller.

The ST-238R needs to be the first, bootable drive. The ST-225 is bootable, but was from eBay and gives an error upon booting up because my computer is too old.

Both drives work separately when set as drive 1 and used as such with the cables. Whenever I try to daisy chain them, however, drive 2 starts clicking and has the light on constantly, and always causes the machine to give a hard drive error.

Is there any way I can get them working? I don't mind losing the data on the ST-225 - I'm going to format it anyway once I can get it working.

 

[modem7]

Looking at http://stason.org/TULARC/pc/hard-di...L-CORPORATION-Two-MFM-ST506-412-driv-227.html you must have the F300/F320 variant of the WDXT-GEN - the one for drives of 615 cylinders and 4 heads, write precompensation cylinder of 307.

The write precompensation of 307 of that card fits well with the ST-225 (WPC of 300), but not with the ST-238R which is not designed to receive any write precompensation. So your ST-238R will get write precompensation applied on cylinder 307 onwards. I really can't say what the impact of that will be, but I expect it to be very minor, and it won't be causing your current problem.

                 WDXT-GEN Controller Board
               ╔════════════════════════════════╗
               ║          ┌────┐       J1       ║
               ║    ┌─────┤ J2 │   ┌─────────┐  ║
               ║    │ ┌───┴────┘   └─┬─────┬─┘  ║
               ║    │ │   ┌────┐     │  C  │    ║
               ║    │ │   │ J3 │     │  O  │    ║
               ║    │ │   └┬─┬─┘     │  N  │    ║
               ╚════■ ■════■ ■═══╗   │  T  │  ╔═╝
                    │ │    │ │   ╚═══■  R  ■══╝
                    │ │    │ │       │  O  │
                    │ │    │ │       │  L  │
                    │ │    │ │       │     │    ST-225 - Drive D:
                    │ │    │ │   ╔═══■═════■═══════════════╗
                    │ │    │ └───■                         ║
                    │ │    └─────■  ( DS1 - unterminated ) ║
                    │ │          ║                         ║
                    │ │          ╚═══■═════■═══════════════╝
                    │ │              │|  | │
                    │ │              │ \/  │
                    │ │              │ /\  │
                    │ │              │|  | │    ST-238R - Drive C:
                    │ │          ╔═══■═════■═══════════════╗
                    │ └──────────■                         ║
                    └────────────■  ( DS1 - terminated )   ║
                                 ║                         ║
                                 ╚═════════════════════════╝

I don't have a WDXT-GEN card, but here's how things will probably work:

If you have a control cable (the wider of the cables) with a twist in it, set both drives to the second 'drive select' position.
If you have a straight-through control cable, set the ST-225 to the second 'drive select' position and set the ST-238R to the first 'drive select' position.

Remove the terminator from the ST-225.

Ensure that the daisy/radial jumper on both drives is set for 'daisy chain' operation.

See how that goes. You may need to low-level format the ST-225 (when it is in as the second drive) using the standard G=C800:5 technique.

Also, some XT controllers require different drive select, and so when using a twisted control cable, you may need to set both drives to the first 'drive select' position.

 

[modem7]

And something to be mindful of is the use of the correct control cable.
I think we had a case here where someone was using a twisted floppy cable instead of a twisted hard drive cable.
The easy way to tell is that the hard drive cable has 5 wires reversed (twisted) whereas the floppy cable has 7 wires reversed.

 

[Rizon]

I believe the problem is the controller cable - it has 7 wires reversed rather than 5, though the cable works fine with my other drive.

I do have another controller cable, however, it only allows for one drive. I have another controller card as well. If I install that in the computer, should I be able to access both drives?

I don't know how the computer would decide which is drive C, though. Would setting the 238R up on the existing controller as drive 1 and the 225 up as drive 2 (via the J2 and J3 connections) work, or not? The second controller is a WD1002A-WX1.

 

[modem7]

I believe the problem is the controller cable - it has 7 wires reversed rather than 5

See http://members.dodo.com.au/~slappanel555/misc/floppy_vs_hard.jpg for a picture showing the difference in the twisted floppy cable versus the twisted hard drive cable.

though the cable works fine with my other drive.

If a hard drive were placed at the end of a twisted floppy cable, some very important signals get blocked. The hard drive can't tell the controller when the heads are sitting on cylinder 0, and the hard drive never gets the signal to select the first head. In one of my (expendable) clone PCs, I tried substituting a twisted floppy cable in place of the twisted hard cable, and as expected, it didn't work. You must have had your drive sitting on the middle connector, before the twist.

I do have another controller cable, however, it only allows for one drive. I have another controller card as well. If I install that in the computer, should I be able to access both drives?

So two controllers in an XT with one drive hanging off each controller. It's possible, but can be complex (take a look at http://stason.org/TULARC/pc/pc_hardware_faq/3_07_How_do_I_install_a_second_controller.html as an example).
You'll have fewer problems with the 'two drives off one controller' scenario.

 

[Rizon]

Yeah, it is hooked up to the port before the twist.

I guess I'll go ahead and order a hard drive cable, though I'll probably wait until I get settled in at college.