exxos's Atari, Amiga & retro forum

Maybe it's over terminated then. Do you have an internal drive?

Atari did say that if you wanted to use external devices you should remove the terminating resistors from the motherboard.

Note that the termination has to be at the end of the bus at both ends, as it's there to prevent the reflection of the signals back along the wires.

@stephen_usher Sorry if I'm not being clear enough, these are internal drives. I am only using one drive at a time.

@Steve

Check if the drive(s) require active powered terminators or not.

SCSI2SD v6:

Active Terminator
V6.0 boards
The terminator is enabled via software configuration using the scsi2sd-util6 tool.

source: www.codesrc.com/mediawiki/index.php/SCSI2SD_UserManual

RaSCSI Tranceiver termination explained

github.com/akuker/RASCSI/wiki/Transceiver-Comparison

From what I see here they both provide active termination.

Ok, if you've got the option, try ALL terminations as powered and then ALL as non powered.

IIRC different (powered<>non powered) terminators can introduce imbalances (similar to not earthing a turntable to an amplifier).

I think, all non powered will be the trick! ;)

@mrbombermillzy Sorry for being a bit dense, when you say all non powered, are you saying disable termination. If they are different things entirely, then I do not know how to enable a 'non powered' termination on these devices.

@stephen_usher may have a point about over termination.

I've seen 50 Pin SCSI setups with very long cables work just fine as long as they were terminated correctly at the HBA and last drive.

I also went out to a server that had 4 HDDs and 2 CDs in the SCSI chain. All were correctly ID'd, however they all had termination enabled and as soon as the last CD drive was connected, somewhere in the middle, all but 2 of the hard drives disappeared from the bus. Once I properly enabled termination at the ends only, so HBA and last HDD, it was all fine.

If the drives are terminated, I'd have a look at the TT docs and check to see what the termination actually does and if it is needed when a device is plugged in at the end of a cable.

Based on the usual SCSI setup, I'd expect it should be, but you never know with Atari.

Steve wrote: 18 Nov 2021 11:38 @mrbombermillzy Sorry for being a bit dense, when you say all non powered, are you saying disable termination. If they are different things entirely, then I do not know how to enable a 'non powered' termination on these devices.

Ok, you have to terminate both ends of the SCSI chain. Full stop. Otherwise you will, like I said, get data signal bounce and therefore corrupt data.

However, some devices provide both active (powered) and non powered terminators.

e.g. I've got an external CDROM for the TT that won't work with the CD-ROMs jumpered (passive) termination and needs a big active block on the SCSI out port.

Forgive me, but it's been a long time and I'm a bit rusty, I can't remember if the TT has active termination internally or not. However, it doesn't matter if you just try active termination on your RaacsSCI/SCSI2SD and see if it works. Then if not, try passive termination.

As an aside, I was under the impression that a v6 SCSI2SD was not TT compatible. I believed that the v5.5 was??

EDIT:

If you don't want active termination on the SCSI device, but that's the only option it gives, you can leave it unterminated and then put the necessary termination type on the next connector on the cable. That should work.

Steve wrote: 18 Nov 2021 11:38 @mrbombermillzy Sorry for being a bit dense, when you say all non powered, are you saying disable termination. If they are different things entirely, then I do not know how to enable a 'non powered' termination on these devices.

Active termination uses additional components to provide active power to the terminator on each device, rather than Passive termination which relies on the power from the SCSI bus which may fluctuate. I've seen drives that have the capability to do either active or passive depending on your needs, and controlled by a jumper.

Because it is actively powered and the voltage is regulated it provides a more stable termination.

Either way, termination ie either off or on, and you need to have it on at the ends of the bus, so host bus adapter (HBA) or last drive in the chain. If you have terminated devices in the middle too, it'll break the chain.

Pin 26 of the 50 pin connector carries terminator power.

Also, if it helps clear things up, the TT SCSI IC is NOT the end of the chain if you don't have board terminators, it's in the middle of the internal/external chain. :)