SCA to *IDE*? Sanity check please.

[Simon_Bitdiddle]

I was searching out a SCA to 50 pin adapter and found this on Amazon: https://www.amazon.com/CERRXIAN-Female-Adapter-Converter-Computer/dp/B09G27DNN4/

It claims to be a SCA to IDE adapter using a 50 pin header. I'm sure it's a typo but... was there a 50 pin IDE standard?

 

[NJRoadfan]

No, its 50-pin SCSI.

 

[mg.man]

its 50-pin SCSI

...and, FWIW, I've *never* been able to get those type adapters to work on a vintage Mac.

If you want an adapter that works, check with @max1zzz. I have a bunch of his and have had good luck with most SCA80 drives

 

[MrFahrenheit]

...and, FWIW, I've *never* been able to get those type adapters to work on a vintage Mac.

If you want an adapter that works, check with @max1zzz. I have a bunch of his and have had good luck with most SCA80 drives

I have some of those, as well as some I tracked down 2 years ago that also work well:

SCA 80 - IDC50 Male Header, w/Active Termination | DataStorageCables

SCA 80 - IDC50 Male Header, w/Active Termination

www.datastoragecables.com

These are the only two that I've found to work. I bought numerous others from numerous sellers and websites before I found any that worked, including max1zzz's and the ones at the DataStorageCables link.

 

[Fizzbinn]

...and, FWIW, I've *never* been able to get those type adapters to work on a vintage Mac.

If you want an adapter that works, check with @max1zzz. I have a bunch of his and have had good luck with most SCA80 drives

Same, at least not with any reliability. You need an adapter with termination as typical (all?) SCA drives don't do this on board the way most 50-pin narrow SCSI drives can. Examples:

 

[MrFahrenheit]

Same, at least not with any reliability. You need an adapter with termination as typical (all?) SCA drives don't do this on board the way most 50-pin narrow SCSI drives can. Examples:

View attachment 42060

In your bottom picture, there are 4 resistor packs. Some SCA 80 to 50 boards have resistor packs, but fewer, and not enough for the number of SCSI lines in a u160/u320 drive, apparently.

 

[NJRoadfan]

The issue is "upper byte" termination. The SCA 80-pin and some 68-pin wide drives need the extra 8 data lines terminated when connected to a "narrow" 8-bit bus.

 

[max1zzz]

In your bottom picture, there are 4 resistor packs. Some SCA 80 to 50 boards have resistor packs, but fewer, and not enough for the number of SCSI lines in a u160/u320 drive, apparently.

The issue is "upper byte" termination. The SCA 80-pin and some 68-pin wide drives need the extra 8 data lines terminated when connected to a "narrow" 8-bit bus.

Yep. Allot of SCA drives (particularly newer U320 ones that where not really designed to work on 8 bit busses) do not work correctly without the upper byte terminated

 

[Fizzbinn]

In your bottom picture, there are 4 resistor packs. Some SCA 80 to 50 boards have resistor packs, but fewer, and not enough for the number of SCSI lines in a u160/u320 drive, apparently.

Pretty sure the top one has active termination as it has a voltage regulator. I know you only need two, 10-pin, 110 ohm resistor packs to terminate narrow, 8-bit, SCSI, so I'm guessing the third 110 ohm resistor pack handles the upper 8 bits of wide, 16-bit, SCSI.

The bottom one has three, 8-pin, 330 ohm resistor packs in sockets and one 10-pin resistor pack that I can't read the resistance markings on. Pretty sure the 330 ohm resistor packs point to passive termination (also don't see a voltage regulator) and three of them can terminate a narrow, 8-bit, SCSI bus. I think the fixed 4th resistor pack is for the upper 8 bits of wide, 16-bit, SCSI. You'd remove the three 8-pin, 330 ohm resistor packs if you wanted to use the SCA drive+adapter in the middle of a narrow SCSI bus.

If you find a SCA 80 to 50 adapter with only one resistor pack (which would be terminating the upper 8 bits of the wide, 16-bit, SCSI bus) its likely intended to be used in the middle of a narrow SCSI bus or in an external enclosure where an external terminator can be used to terminate the narrow, 8-bit, SCSI if its at the end of the chain.

The issue is "upper byte" termination. The SCA 80-pin and some 68-pin wide drives need the extra 8 data lines terminated when connected to a "narrow" 8-bit bus.

If the SCA drive is at the end of the narrow SCSI chain I'm fairly certain it needs both the upper and lower bytes terminated, upper terminates the unused wide SCSI data lines and lower terminates the data lines in use on the narrow SCSI bus.

But if the SCA drive is in the middle of the narrow SCSI chain you would want the adapter to only terminate the unused upper byte wide SCSI data lines.

 

[Unknown_K]

There is a difference between 50 pin and 68 pin SCSI termination and SE and LVD controllers.

SCA has no termination by design so most adapters didn't bother with it either assuming you would terminate on the cable ends.

I never had much problem with SCA drives on macs because I only used cabled with termination on the ends (mostly 68 pin but 50 pin terminators exist).

If you are using more then 1 drive on each cable you have these rules to live by:

All About SCSI

The DataPro 'All About SCSI' is an in-depth resource for answers to all types of SCSI questions.

www.datapro.net

SCSI DEVICES THAT DO NOT WORK TOGETHER​

The SCSI standard contains various alternatives which are mutually exclusive within a system (or a bus).
These mutually exclusive alternatives are:

1. Single - ended or differential
2. Termination power supplied by the cable or not
3. Parity implemented or not
4. "Hard" RESET or "Soft" RESET
5. Reservation queuing implemented or not

This means that the two devices you connect with a SCSI cable must be compatible, or of the same type, in terms of each of the five features listed above. For instance, both devices should be differential or both should be single - ended; At the same time, both should have a "hard" RESET or a "soft" RESET and so on...for each of the five features above.
You can find out what features your SCSI devices have by reading the STATEMENT OF CONFORMANCE with the standard in the device documentation.

 

[ScutBoy]

On the adapters with no termination resistors present, I've had good luck using inline terminator - cable->terminator->drive.

one example:

50pin/wire Internal Male~Female cable/cord Terminator SCSI1/2 HD/HDD/CD Drive$SH | eBay

SCSI Internal 50-pin (aka IDC50) Male to Female. Need an Internal Cable with this connector?. Need other Internal SCSI Adapters?. Need Internal SCSI Cables?. Picture shows 2, you get 1. for use with PC, Mac, Sun etc.

www.ebay.com

 

[Compgeke]

There are a couple ways to get around termination issues:
1.) Get 50 to 68 pin adapters, and slap those into your 50 pin devices and motherboard. Run a 68 cable.
2.) Get one of the adapters with both 50 and 68 pin connectors, and slap a 68 pin terminator on it.
3.) Certain Seagate and IBM SCA drives have terminators built in.