Need a control cable (the 34 pin cable) which is capable of controlling 2 (or more) MFM hard disk drives, in particular a Seagate ST-225 and a ST-251. Current cable I'm using only has connectors to control one hard disk and I would like to use the two simultaneously. Thanks.
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Control cable for 2+ MFM hard disk drives
- Thread starter Hoss4272
- Start date
DonutKing
Experienced Member
You can make one out of your existing single cable, if you can find a spare edge connector. Just crimp it on to the middle of the cable. Install the second drive on the middle connector, jumper it for Drive Select 2 and remove the terminating resistor. The drive on the end should have the resistor installed and jumpered for DS1.
Some cables had a twist in them but this was optional - it was just so you could jumper both drives to DS2 (made it quicker and easier to install). If your cable doesn't have the twist, set the end drive up as DS1 as mentioned above.
You could also make one out of a floppy cable if you cut off the end with the twist in it (floppies have different wires twisted compared to MFM drive controllers so don't try to use the connectors after the twist).
Some cables had a twist in them but this was optional - it was just so you could jumper both drives to DS2 (made it quicker and easier to install). If your cable doesn't have the twist, set the end drive up as DS1 as mentioned above.
You could also make one out of a floppy cable if you cut off the end with the twist in it (floppies have different wires twisted compared to MFM drive controllers so don't try to use the connectors after the twist).
Stone
10k Member
Or, you could rework a floppy cable and remove the floppy twist and add the twist necessary for a HD cable. That twist is wires 25 thru 29. Or from the other (easier) side to count from, twist wires 6 thru 10.
If all else fails, lemme know where you are as I might have one to spare. I know I have one 'cause I'm looking at it.
If all else fails, lemme know where you are as I might have one to spare. I know I have one 'cause I'm looking at it.
Chuck(G)
25k Member
..or simply not bother to twist the cable at all--just change the drive select jumpers. Unlike the floppy cable, the twist in the hard cable involves drive select only--and those can easily be changed on the drive itself. The floppy cable also includes the motor control lines, which aren't present on a hard disk. So "flat all the way" is perfectly okay.
MikeS
Veteran Member
Unlike Cable-select IDE drives it doesn't really matter which drive goes where, as long as they're appropriately jumpered and the (only) terminating resistor is installed in the drive at the end of the cable (and the Data cables go to the appropriate drive).
Odd though; I'd have thought that the second 20 pin data cable would be the one that's hard to find/make; if the OP actually had two sets of both then it should be pretty simple to carefully remove the 34 pin edge connector from the second control cable and crimp it on to the other cable with a vise or even vise grips.
Good luck with the "two (or more)" part BTW; two's usually the limit for most controllers...
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kb2syd
Veteran Member
In the PC world maybe. I was using four on one controller in the 80's on a Tandy 6000.
modem7
10k Member
IDC type connectors are designed for one-time use only. That doesn't mean that it's impossible to reuse them, but it does mean that sometimes one ends up with an intermittent cable. It's just a risk that people need to be aware of.
Chuck(G)
25k Member
I've got a bunch of extras, but I don't know where you live. If, for example, you live where Tezza lives, it's not cost effective for you.
MikeS
Veteran Member
I've got boxes full as well but I gave up; if people can't be bothered to tell us what part of the world they're in then I can't be bothered asking any more.
MikeS
Veteran Member
Interesting; I've got lots of non-PC systems and HD controllers and most of them will handle 4 floppies, but I can't say I've ever seen an MFM hard disk controller with more than two data connectors (although you could have more than two HDs with more than one controller of course); live and learn.
Compgeke
Veteran Member
We need to know how much shipping would be. Say you lived in Brazil shipping would be insane but knowing where you live (Arizona) it's easier to know how much shipping would be if someone were to send you a cable.
I hear it's hot there in Phoenix, my grandparents live there and are always talking about how much cooler California is...Napa anyways.
I hear it's hot there in Phoenix, my grandparents live there and are always talking about how much cooler California is...Napa anyways.
Chuck(G)
25k Member
PC-AT controllers use the IBM 5170 Western Digital controller model, where only a single bit in the task (bit 4 in the SDH register) file is allocated to a drive. Any other scheme would be incompatible at a hardware level and most BIOSes wouldn't work with it. Similarly, IDE and ESDI drives also follow this convention. Otherwise, there's no practical reason that you couldn't put 4 MFM drives on a single control cable if the controller supported individual data cables.
On the other hand, SCSI allows many devices per cable, which goes some way toward explaining its early popularity on high-end workstations and servers.
MikeS
Veteran Member
Well, hardly "fury"...
If you lived relatively close and it didn't involve international shipping I'd gladly offer to pop one in the mail this afternoon; on the other hand, if you lived in New Zealand I wouldn't even bother to reply on the assumption that someone closer will offer one for a lot lower and faster shipping or that you could even buy a new one for less locally and I'd just be wasting my time replying.
Maybe I'm not the only one who doesn't bother replying unless it's obviously close enough to be practical...
What's up with not putting in your location when you're asking for something to be sent to you so you don't waste the time of people on the other side of the world? Never hurts to be considerate, especially when you're asking strangers for a favour...
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MikeS
Veteran Member
Indeed; no technical reason; I've got MFM controllers that do support > 2 drives (40-pin IMI interface), but I've just never actually seen any ST412/506 types.
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Chuck(G) wrote:
PC-AT controllers use the IBM 5170 Western Digital controller model, where only a single bit in the task (bit 4 in the SDH register) file is allocated to a drive. Any other scheme would be incompatible at a hardware level and most BIOSes wouldn't work with it. Similarly, IDE and ESDI drives also follow this convention. Otherwise, there's no practical reason that you couldn't put 4 MFM drives on a single control cable if the controller supported individual data cables.
On the other hand, SCSI allows many devices per cable, which goes some way toward explaining its early popularity on high-end workstations and servers.
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Pretty much what I am looking to do here, Chuck. The controller I have for my TI-99 is a Myarc HFDC (Hard and Floppy Disk Controller) which has 3 data cable inputs, so I could potentially run up to three MFM drives if I had the appropriate control cable. This particular controller can also handle up to 4 floppies. Right now I have the controller connected to a ST-225 and two 360k floppies, and I am running my telnet BBS off this computer. The 20mb Seagate is starting to get tight so looking to add a 40mb ST-251 to the chain.
Chuck(G) wrote:
PC-AT controllers use the IBM 5170 Western Digital controller model, where only a single bit in the task (bit 4 in the SDH register) file is allocated to a drive. Any other scheme would be incompatible at a hardware level and most BIOSes wouldn't work with it. Similarly, IDE and ESDI drives also follow this convention. Otherwise, there's no practical reason that you couldn't put 4 MFM drives on a single control cable if the controller supported individual data cables.
On the other hand, SCSI allows many devices per cable, which goes some way toward explaining its early popularity on high-end workstations and servers.
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Pretty much what I am looking to do here, Chuck. The controller I have for my TI-99 is a Myarc HFDC (Hard and Floppy Disk Controller) which has 3 data cable inputs, so I could potentially run up to three MFM drives if I had the appropriate control cable. This particular controller can also handle up to 4 floppies. Right now I have the controller connected to a ST-225 and two 360k floppies, and I am running my telnet BBS off this computer. The 20mb Seagate is starting to get tight so looking to add a 40mb ST-251 to the chain.