VOGONS


First post, by Swiego

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If my one or two devices connected to an IDE cable are jumpered explicitly for Master/Slave, does it matter which connector (in a 3-connector IDE cable) is connected to the motherboard? Could it be either end? Better yet, the middle connector?

Secondary question, does the answer to the above question(s) change depending on 40- vs 80-pin?

Reply 1 of 11, by derSammler

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You can not connect the middle connector to the mainboard, because IDE is a bus and hence should not have a star topology. Which end you use doesn't matter, however, as the cable is symmetrical and will work both ways. But I would not recommend that, because the connectors are facing the other direction then, of course.

For 80-pin cables, this is different due to cable select line. These are keyed (so they don't fit the "wrong" way anyway) and color-coded and can only be used with the black connector on the mainboard, the blue one on the master, and the grey one on the slave. Also, do not use 80-pin cables for non-UDMA devices, as they may introduce malfunctioning otherwise.

http://retro-net.de/blog.html

Reply 2 of 11, by Swiego

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derSammler wrote on 2020-04-05, 19:36:

For 80-pin cables, this is different due to cable select line. These are keyed (so they don't fit the "wrong" way anyway) and color-coded and can only be used with the black connector on the mainboard, the blue one on the master, and the grey one on the slave. Also, do not use 80-pin cables for non-UDMA devices, as they may introduce malfunctioning otherwise.

Questions,
1) does this mean for 80-pin I can connect the center connector to the motherboard?
2) what if my motherboard’s connector doesn’t not have the black shroud but does have one pin missing?

Reply 3 of 11, by derSammler

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1) no - as stated, the 80-pin cable can not even be used the other way around
2) the missing pin is the key for the 80-pin cable, should you use UDMA devices that require it

http://retro-net.de/blog.html

Reply 4 of 11, by mpe

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It depends.

Devices can be configured as "Master" or "Slave". When set it like this the order doesn't matter. However a device can be also set to "CS" (Cable Select) mode where Master will be on the middle connector and Slave device is on the connector towards the end. But this also depends on the actual wiring of the cable so it this can also be the other way around.

Last edited by mpe on 2020-04-05, 20:43. Edited 2 times in total.

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Reply 5 of 11, by Swiego

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It definitely works with a 40 pin cable with the center connector attached to the motherboard and the ends to a hard drive and optical drive. Both are working properly in Windows 98.

When I replace this 40 pin cable (which has no housing orientation key nor blocked pin socket) with an 80 pin cable (which has both) then only one device is recognized if the center connector is attached to the MB. Well, only the hard drive. It boots fine. If I add the optical drive to the other side I get a controller failure.

Last edited by Swiego on 2020-04-05, 20:38. Edited 1 time in total.

Reply 6 of 11, by derSammler

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Devices can be configured as "Master" or "Slave". When set it like this the order doesn't matter.

Yes, but the hard-wired cable-select lines of the 80-pin cable are the reason why the connectors are no longer equal. Of course you are not forced to use CS on the devices.

http://retro-net.de/blog.html

Reply 7 of 11, by derSammler

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Swiego wrote on 2020-04-05, 20:37:

It definitely works with a 40 pin cable with the center connector attached to the motherboard and the ends to a hard drive and optical drive. Both are working properly in Windows 98.

When I replace this 40 pin cable (which has no housing orientation key nor blocked pin socket) with an 80 pin cable (which has both) then only one device is recognized if the center connector is attached to the MB. Well, only the hard drive. It boots fine. If I add the optical drive to the other side I get a controller failure.

Again, you can't do that. It's like running SCSI with no termination. It may seem to work if you are lucky, but you are creating something here that is no longer within electrical specs and causes bus/parity errors at least. And on the 80-pin cable, each connector has a dedicated function - they are not equal.

Why would you even want to connect the middle connector to the mainboard..? If it is too short otherwise, get a proper cable instead.

http://retro-net.de/blog.html

Reply 8 of 11, by mpe

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If you want to build "Cable Select" cable from straight 40-pin cable you need to interrupt the 28th wire between the middle and end connector.

All 80-wires cables I've seen were already modified for CS operation and they usually had Master and Slave connectors labeled or colour coded.

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Reply 9 of 11, by Swiego

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derSammler wrote on 2020-04-05, 20:41:

Again, you can't do that. It's like running SCSI with no termination. It may seem to work if you are lucky, but you are creating something here that is no longer within electrical specs and causes bus/parity errors at least. And on the 80-pin cable, each connector has a dedicated function - they are not equal.

Why would you even want to connect the middle connector to the mainboard..? If it is too short otherwise, get a proper cable instead.

The computer I was working with was setup this way (OEM config). When I got it and took it apart, I had a memory that it was setup with the center connector attached to the MB, but I neglected to make a note of it. After cleaning testing restoring all components I realized the original IDE cable was not long enough to connect everything if I tried as you described. I also found other posts online from years past hinting at the same. So I posted.

Now I realize it actually does work, and computers came this way at least with a 40 pin cable, and I’ve buttoned the system up. If I get to the point that I need an 80 pin cable I’ll surely look for one with connectors more widely spaced out.

Reply 10 of 11, by Horun

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Swiego wrote on 2020-04-05, 21:54:

The computer I was working with was setup this way (OEM config). When I got it and took it apart, I had a memory that it was setup with the center connector attached to the MB, but I neglected to make a note of it. After cleaning testing restoring all components I realized the original IDE cable was not long enough to connect everything if I tried as you described. I also found other posts online from years past hinting at the same. So I posted.

Is it a Compaq by chance ? I have seen them do some very odd cabling in the past. One example is not using a twisted floppy cable and yet it worked unless you replaced the cable with a standard floppy cable with twist at the end.

Hate posting a reply and have to edit it because it made no sense 😁 First computer was an IBM 3270 workstation with CGA monitor. 🤣

Reply 11 of 11, by maxtherabbit

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derSammler wrote on 2020-04-05, 20:41:
Swiego wrote on 2020-04-05, 20:37:

It definitely works with a 40 pin cable with the center connector attached to the motherboard and the ends to a hard drive and optical drive. Both are working properly in Windows 98.

When I replace this 40 pin cable (which has no housing orientation key nor blocked pin socket) with an 80 pin cable (which has both) then only one device is recognized if the center connector is attached to the MB. Well, only the hard drive. It boots fine. If I add the optical drive to the other side I get a controller failure.

Again, you can't do that. It's like running SCSI with no termination. It may seem to work if you are lucky, but you are creating something here that is no longer within electrical specs and causes bus/parity errors at least. And on the 80-pin cable, each connector has a dedicated function - they are not equal.

Why would you even want to connect the middle connector to the mainboard..? If it is too short otherwise, get a proper cable instead.

That is not correct. IDE is an unterminated bus and you can connect any device (including the motherboard) to any connector on the cable with no ill effect.