Scsi terminator placement...

[Jose]

I got this 68 pin SCSi cable from eBay for my A4000 but the bloody thing has an undetachable terminator in one end (well till I cut it off that is). The termination needs to be at both ends of the chain IIRC so this won't work if I use more devices than the cable allows (i.e. adding an internal to external adapter and prolong the chain with more external devices like DVD burner and external HD) ?

:pint:

[Thomas]

If dealing with 68 pin SCSI cables, you probably have a CSPPC. This one is not terminated internally but needs a real terminator on the cable. So IMHO your cable is ideal: Term - CSPPC - internal devices - external devices - Term.

Only if you want to plug the CSPPC between the internal and external devices you need to cut off the terminator.

Remeber that the adapter from 68 to 50 pins needs to terminate the remaining lines.

Bye,
Thomas

[Jose]

Wish I had a CPPC (it's still on my plans though). I have a WarpEngine wich has a 50 pin scsi2 header. But I decided to get the 68 pin cable anyway, I already have a F-F 50 to 68 adapter, it will serve me the day I get a CSPPC. With what I have now I don't think the remaining lines need to be terminated.
If the terminator on the WarpEngine could be turned off I could use the one on the cable, like the CPPC setup you described above, but unfortunately there seems to be no jumper to turn it off (already checked the manual).

[tonyvdb]

You only need one terminator on the cable. Dont get carried away with multiple terminatores on both ends. I only have one (just like Yours)and it is located on the end of the cable and everything works just fine. If your adding an external SCSI devise then just add the adapter somwhere in between an run it out the back of your case.

[Jose]

@tonyvdb
"...If your adding an external SCSI devise then just add the adapter somwhere in between an run it out the back of your case."
That config would be awkward. Are you sure that would conform to termination rules ? Just to make sure we're talking the same thing, it would look like this:
(- WE stands for WarpEngine, T for terminator)

Code: [Select]

WE(T)--CableNode1--Node2--Node3--Node4--T
                     |      |      |
                     |      |      |
                    HD    DVD    ExternalAdapter
                                   |
                                   |
                                  DVD Burner1
                                   |
                                   |
                                ExternalHD
                                   |
                                   |
                                DVD Burner2
                                   |
                                   |
                                  etc.code

[tonyvdb]

Its always worked for me. I have never used more then one Terminator and have always placed it on the end of the cable or on the last connector of the cable.
I then place however many devices I want on the remaining connectors. So adding an external SCSI conector to the cable somewhere in between should work as well.

They also make pasthrough active terminators so you dont waste any of the "nodes" on the cable.

Note: alot of external SCSI devices have a jumper to enable or disable the on board termination so if you put this device at the end of the cable and remove the terminator that you have and then enable the termination on that device it should work.

[Jose]

Got the drawing to display correctly...

I guess it's better to try it then cut off the terminator, as it's gonna be usefull if I ever get a CSPPC.

Cheers

[tonyvdb]

its actualy intresting to be talking about this because with My Video Toaster Flyer system I have 7 SCSI drives spred over 3 SCSI chains and do not have even one terminator on the cables. I am thinking that there must be an on board terminator on the Flyer board its self in order for this to work but have never found out for sure.

[patrik]

@Jose:

Keep the terminator and place it at the WE-end and remove the termination from the WE. The UW-terminator is of the active type, compared to the passive type terminator on the WE plus it terminates the whole wide bus, compared to the WE which would leave the upper byte unterminated.


/Patrik

[Jose]

@Patrik
"Keep the terminator and place it at the WE-end and remove the termination from the WE. ..."

I just read the manual and the only thing related to disabling termination on the WarpEngine is a jumper (Jumper1) that disables termination power. However if the card has termination resistors (apparently most cards had them but some didn't) they won't be disabled.
 
Will just disabling termination power be enouph ?

If not this will probably cause all kinds of problems cause the chain will be terminated right at it's beginning.

[SyrTran]

@tonyvdb

its actualy intresting to be talking about this because with My Video Toaster Flyer system I have 7 SCSI drives spred over 3 SCSI chains and do not have even one terminator on the cables. I am thinking that there must be an on board terminator on the Flyer board its self in order for this to work but have never found out for sure.

If you check, you will probably find that the last drive on each chain has its on-board termination enabled.  This is a feature of most SCSI drives.

I just checked mine, and they're definitely set.  IIRC, the Flyer doesn't work right if the chains aren't terminated.

[tonyvdb]

Nope, Non of the drives are terminated. I checked

[patrik]

@Jose:

Atleast on my WE the three termination-resistor-packs are socketed and to disable the WE onboard termination you just have to remove them.

The termination power should not be disabled as the terminators on the scsi-chain needs power atleast from one source.

I dont really understand what you mean with: "If not this will probably cause all kinds of problems cause the chain will be terminated right at it's beginning.", but I can say that if you remove the termination resistors from the WE and thus disable its termination, it will be perfectly fine to connect the termination end of the UW-cable to the WE (using that adapter).

Also, as I said earlier about terminating the whole width of the bus. If you use UW-drives, you also need to terminate the upper byte of the bus, which the WE cant, unless your adapter includes upper byte termination. The terminator attached to the UW-cable will terminate the entire bus-width plus it is an active terminator, whilst the WE-terminator is passive, which is more or less crap for the integrity of the signals on the bus.

Keep in mind though that your adapter should be without upper byte termination for this to work ok, or else the upper byte will be double-terminated. Most F-F 50<->68 adapters doesnt include this, but it might be worth checking out.

Check this page for a lot of good and rather detailed info about SCSI termination, termination power, 50->68 and 68->50 adapters etc.


/Patrik

[Jose]

@Patrik
That's one awesome site!

@All
I only have one doubt left. If there are multiple "daughter" chains connected to the main scsi cable that comes from the scsi host adapter, do you have to terminate each one of them ? According to that site Patrik posted and others I've googled, the termination must only be made on two places. Maybe that's assuming there are no multiple chains. If not then SyrTran has his termination badly done.

[Jose]

BTW, thanks for pointing out the resistors on the WE can be taken off, the manual doesn't clearly say that and I wasn't sure...