SCSI Terminators - active or passive?

[Fred Martin_1]

What criteria determines which type of terminator to use on the end of a SCSI chain?

White papers here suggest that it's length alone - more than 3 meters would use an active terminator.

[Dan Hetzel · Accepted solution]

Hi Fred,

If you have both at hand, use active terminators as they will guarantee proper termination (and signal level) for up to the maximum cable length.

For short cables (less than 10') you may use passive terminators.
I'm always using active terminators, independantly of the SCSI bus length.

Best regards,

Dan

[paul courry]

A suggestion. Think of the guy who will take over your job at some point in the future. If you mix passive and active and they are not smart enough or experienced enough to perceive when each type is appropriate they will end up cursing you when things stop working.

Go with active throughout your system, the guy who gets your job will get more sleep.

[Michael Lampi]

Passive terminators are effective up to the full 6 meter length of "slow" (5 MHz) single
ended SCSI buses, as is used on HP's narrow
SCSI bus available on most of its workstations
and servers.

Active terminators can be used without harm on
these buses as well.

When you go to faster SCSI buses, then you will
need the better signal margins that an active
SCSI terminator provides. This includes most
Fast (10MHz) buses. While passive terminators
will work on shorter Fast buses, they are not
adequate on longer buses.

For Ultra (20MHz) SCSI buses you need to use
Forced Perfect active termination, and really
pay attention to eliminating all excess cable
length.