SCSI questions

[darkcoder]

Hello

I live happliy with 3 diferent SCSI chains (not all on the same Amiga :-), which all works
nicely with current settings:
 - Cybertorm 3 UW controller, with 2 UW HD
 - A4000T on board SCSI-2, with CDRW, CDR, HD
 - WArpEngine SCSI-2, with CDRW, HD

However, some days ago, I learnt from another thread (now I can find it anymore) that TERM Power
does not imply Termination Enable. So I decided to check my SCSI chains. I also studied some
docs in italian language about SCSI, from which put under my nose more questions.

Q0) I learnt about SE, HVD and LVD electrical interfaces. None of my 3 controllers mention which
interface it support. Am I right in assuming (because of the age) that all of them use SE
interfaces?

Q1) Termination. As we all know, the Cyberstorm controller has no terminator. For this reason I
put it in the middle of the chain. At one end of the chain I put a Quantum Atlas 2 HDD with
Termination Enabled. At the other end a Fujitsu MAH3091MP. This HD is a LVD drive, but can work
also in SE mode. However, it does not have a TE jumper,although it has a Term Power enable
jumper. This would mean that my chain is not correctly terminated! :-( However it worked nicely
for years! How is it possible? Am I in danger of some hardware damage?

Q2) TERM Power. Here I am puzzled. How should I set TERM Power? The Cyberstorm docs says that one unit should provide TERM Power(I guess the Cyberstorm itself doesn't). The A4000T doc does not mention the issue, while WarpEngine can provide TP. In one chain, how many units have to provide the power?

Q3) Parity Check. The italian language docs, say that Parity Check should be enabled or disabled uniformly on all devices  in a chain (all enabled or all disabled). For me this is tricky because some device (AFAIK, I don't have complete docs for any device) doesn't do it, some does always, and some can be enabled/disabled via jumpers.
Moreover, none of my 3 controller mentions this issue. What should I do?

Many thanks for your help!! :-)

[Nataline]

Q1) This would mean that my chain is not correctly terminated! :-( However it worked nicely
for years! How is it possible?

Blind luck, perhaps?

Am I in danger of some hardware damage?

I don't think so. In danger of data corruption, yes. Hardware damage, hardly.
(If someone more experienced thinks I'm wrong on this, please point out my mistakes before people start losing their drives just because I didn't know about some obscure Set_Device_On_Fire command or something.;-))

Q2) TERM Power. Here I am puzzled. How should I set TERM Power? The Cyberstorm docs says that one unit should provide TERM Power(I guess the Cyberstorm itself doesn't). The A4000T doc does not mention the issue, while WarpEngine can provide TP. In one chain, how many units have to provide the power?

I read a bit about Term Power and now I'm puzzled too. It seems my CSPPC driven chain has also survived on blind luck all these years - I don't think I've ever had anything providing Term Power. :-?

According to this only one Term Power provider is required.

To either clarify or further confuse on the subject of SCSI termination, I offer this.

[Dandy]

darkcoder wrote:

Hello
...
Q1) Termination. As we all know, the Cyberstorm controller has no terminator. For this reason I
put it in the middle of the chain. At one end of the chain I put a Quantum Atlas 2 HDD with
Termination Enabled. At the other end a Fujitsu MAH3091MP. This HD is a LVD drive, but can work
also in SE mode. However, it does not have a TE jumper,although it has a Term Power enable
jumper. This would mean that my chain is not correctly terminated! :-( However it worked nicely
for years! How is it possible? Am I in danger of some hardware damage?

Q2) TERM Power. Here I am puzzled. How should I set TERM Power? The Cyberstorm docs says that one unit should provide TERM Power(I guess the Cyberstorm itself doesn't). The A4000T doc does not mention the issue, while WarpEngine can provide TP. In one chain, how many units have to provide the power?
...

I seem to remember from the time when I sat up my SCSI chain (1998) that the documentation of my CyberstormPPC said something like "do not use the internal terminators of the devices - use external, active terminators instead".

That's what I did.

My chain looks like this:

act. terminator -> 160gB IDE HD via ACARD UW-SCSI to IDE bridge -> 4.3 gB UWSCSI HD -> CSPPC -> IDE DVD-RAM via ACARD UW-SCSI to IDE bridge -> SCSI II CD-ROM via UW->SCSI2 adaptor -> SCSI II CD-RW via UW->SCSI2 adaptor -> SCSI II tape streamer via UW->SCSI2 adaptor -> UW to SCSI2 adaptor, actively terminating the upper 8 bit -> slot bracket -> ext. SCSI 2 scanner -> act. SCSI 2 terminator (actively terminating the lower 8 bit)

[Ral-Clan]

You can buy internal pass-through 50 pin active terminators.  If your final device does not have termination (which seems strange to me), you put this device in between the ribbon cable and the drive.  You can buy active and passive versions on Ebay.  I would recommend the active version.

Alternatively, you can buy a ribbon cable with multiple connectors on it, connect your last drive to the second last connector on the cable, and use an internal active terminator on the final connector of the cable.

[darkcoder]

Many thanks to all for the info, especially the docs linked by nataline are very interesting.

@Dandy: you are right that the Phase5 manual specifies to use ACTIVE terminators, but as far as I remember it shows an example of SCSI chain where at one end there is a HDD with on-board active terminators. So, I am not sure that on-board == passive. It seems that for an Ultra SCSI bus active termination is required, so I was assuming that onboard terminators of Ultra HDD were all active.
Now I am not sure at all, so I think the best thing I can do is to buy a pair of active terminators.

regards

[zipper]

 so I was assuming that onboard terminators of Ultra HDD were all active.
Now I am not sure at all, so I think the best thing I can do is to buy a pair of active terminators.

I think so; they are rare but my SG UWSCSI 68pin HD has working termination, so just the other end needs an active terminator thingie.

[Zac67]

LVD/SE devices usually lack termination options - you'll have to use an external (to the device) terminator or connect it to the middle of your SCSI bus.

Term power has to be provided by at least one device, otherwise termination doesn't work at all. It provides electrical power for all (=both) active/passive terminators on the bus, hence the name.
In theory it doesn't hurt setting up a lot of devices to provide term power BUT in real life I've seen e.g. NCR host adapters screwing up that way. A good way to do it: For short busses (<=1m) and few devices (<=3) use one term power source. For longer/more complex setups use two term power sources at the ends or near the ends (when those vary).

@darkcoder
Ultra SCSI requires active termination, so all ultra drives carry active ones (if at all).
Passive terminators are resistor arrays that look like a little comb (usually two or three) and have to actually be removed from the PCB - attach them to the device, not all are alike!
Active ones come in IC form and there's a jumper to de/activate them.
External terminators are marked; if there's no mark, they're passive.