User`s manual

7-33
Theory of Operation
SCSI Termination
SCSI termination for SmartRAID V controllers is controlled through
Storage Manager or SMOR. Refer to Chapter 3, “Configuration and
Installation” for information about setting SCSI termination for
SmartRAID V controllers.
SmartRAID V controllers contain onboard active SCSI terminators for
maximum reliability with Fast and Ultra SCSI devices. Active termination
for a single-ended bus uses one 110Ω resistor per signal, pulled up to a
locally supplied voltage that is regulated at 2.85V. Active termination for
Ultra2 SCSI uses a differential impedance of 100Ω with a 1.25V bias.
Features of active termination include:
• Better immunity to fluctuations in TERMPWR.
• Closer match to the characteristic impedance of the cable minimizes
reflections.
• Increased signal-to-noise ratio.
Passive termination employs one 220Ω pull-up and one 330Ω pull-down
resistor per signal. Active terminators should be used whenever possible.
However, active and passive termination can be mixed on a SCSI bus and
will result in better reliability than using only passive termination.
IMPORTANT
Do not use passive termination for Fast-20 or Ultra SCSI in a single-ended
bus configuration.