[weblacky]

HI All,
I’m posting today about the SCSI ID connector found on the Indigo2 3.5” and 5.25” drive sleds. Please note that I believe this connector is missing on the Floptical Drive sled (at least it’s trimmed off on mine).

Now, I’ve never found any documentation about this connector. I have seen the flexible drive cable designed for SGI provided drives, but this doesn’t really help in all situations. So I decided to pin it out and use the sled connector on my drives…short answer…it works great! I’ll detail what I found here so you can do this at home!

Please note, I’m not going explain how SCSI IDs work, so I’m going write this with the assumption you know how to set a SCSI ID. Please search online for explanations of how SCSI ID pins are used if this topic isn’t familiar to you.

The Indigo2 was designed to have a known SCSI ID assigned to each bay, but very few people could use the connector to make that happen. I have quite a few drive sleds and using this method, I can be assured that when I place a drive in a slot, I know what the ID will be and it will be consistent with what the machine PROM defaults.

The Sled ID connector is a normal Dupont 3.5mm header connector 3x2 (female) and will fit correctly on most Optical drive SCSI headers (with pin swapping, I’ll explain later).

Most hard drives (that use micro-jumpers) use a Dupont 2.0mm connector, so you’ll have to create a simple (but tiny) adapter cable if you want to cable directly to a drive. You can also get a premade male 3.5mm connector and solder the wire ends to a SCA bridge adapter jumper area to automate the SCSI IDs on a SCA adapter used on the Sled (done this twice now, see pictures).


I’ve attached a VISIO orthographic drawing of the sled connector and the pin assignments. Please note, that the lower (bottom three) holes only have one wire and only that hole (with bottom single wire) has a ground connection. That’s the ground in the ID system, the other pins are the ID bits. Most of the time, this connection will seem backwards in natural assignment.

For Optical drives, I’d suggest looking up ID assignments in the optical drive’s datasheet and also use a multimeter set on continuity to find which side of the assignment pins is ground.

Let me be clear, POLARITY matters! While it shouldn’t damage a drive, the wrong polarity will give weird ID assignments (not what’s expected). The pins for the three ID bits (columns) each have a ground, all grounds are usually tied together. So just check continuity between neighboring pins within the ID group of the drive’s ID setting connector. You find that likely all the ground pins on the ID connector are electrically connected…that shows you which side is to be connected to the sled ID connector ground. Also…since they are all connected together…connecting the ground line to ANY ONE of the these ground pins will work for ANY ID pin(s). So you don’t often need to connect all ID pins to their associated grounds. If you find all grounds have continuity with each other, then any single ID ground will work with ANY combination of ID pins.

I also label the sled ID connector wires before ANY modification. I recommend using a permanent marker (sharpie) and making “slashes” across the wire so put three slash (III) across the first wire ID2, (II) on the second ID1, then (I) on the third ID0. Now you can fiddle with them and know which wire has what function!

So after verifying which side of the ID connector has ground on your optical drive (I’ve found more often, the lower (towards the bottom) of the optical drive pin row, of the 3 ID pin columns, is ground), then to use the sled ID connector, simply pull out and swap sled ID connector wires for ID0 and ID3.

To do this you, gently, use a pin and push down the gold finger on the top of the connector for the line you want to remove. Push down with the pin and pull gently on the wire and the crimped connector should come out the back of the sled ID connector, then swap its position with the other side (ID0->ID2 position, ID2 -> ID0 position). With this reassignment, you’ve now logically rotated the top ID bits by 180 degrees. Now they match the ID assignment pins and ground of your optical drive!

Then insert the entire connector onto the optical drive ID selection region, starting with the first ID. On drives where the ID has more than 3 pins (columns) because they are UW SCSI or better, put the connector the first three ID columns only.

Don’t HOT SWAP an Indigo2 sled…ever…so check by powering down the station, inserting the sled(s), and booting to prom and check with an HINV. It should show their SCSI ID next to each entry.

A normal Indigo2 uses ID 1 for the booting (hidden) 3.5” bay, ID 2 for the accessory 3.5” bay, and ID 3 for the optical drive bay.

If you see ID 6 for optical drive…your connector hasn’t been pin swapped correctly, recheck ID pins for ID0 and ID2 have swapped positions on the connector.


For Hard drives, you’ll almost never be able to use the 3.5mm sled connector to attach to the drive (though I have found some SCA bridges use them instead of micro jumpers). For this I got a small section of “zippable” ribbon cable and crimped and made up 3.5mm male connectors to 2.0mm female connectors (drive side). One-to-one is all you need. I split them up into two connectors because you’ll never know the ID bits polarity of a drive (they do change with each drive!).

Place the ID pins on their own 3x1 DuPont connector, place the ground on a single pin connector or whatever you can get. Then you can rotate the ID connector 180 degrees for drives headers that go ID2, ID1, ID0 instead of ID0, ID1, ID2. Either way you’re covered.


Finding the 2.0mm connectors and housing wasn’t easy…I ended up buying from an eBay supplier in China to get mine and I never found any kind of part number or anything. So I can’t help much in the sourcing of these connectors. You can get full kits (less the crimper) on Amazon for 3.5mm DuPont header connectors (to mate to the Sled ID Connector). Drive side is much harder.

With later stations using SCA connectors, this was all built-in to the chassis, for older systems it was a connector on the sled. Since many people are getting SCA drives as upgrades for their SGIs, I suggest doing this modification on a SCA adapter bridge (as the parts are easier to get and it’s a cleaner look).

Hopefully this post is helpful to all the Indigo2 owners and provides you with a fun project.

As always, have fun with your SGIs,

-Josh