Scsi Bus Termination; Problems On The Scsi Bus - ADIC Scalar 100 User Manual

Notes:
1. The listed maximum bus lengths may be exceeded in Point-to-Point and engi-
neered applications.
2. Use of the word "Narrow", preceding SCSI, Ultra SCSI, or Ultra2 SCSI is
optional.
3. Low Voltage Differential (LVD) was not defined in the original SCSI standards
for this speed. If all devices on the bus support LVD, then 12-meters operation
is possible at this speed. However, if any device on the bus is singled-ended
only, then the entire bus switches to single-ended mode and the distances in
the single-ended column apply.
4. Single-ended is not defined for speeds beyond Ultra.
5. HVD (High Voltage Differential) is not defined for speeds beyond Ultra2.
6. After Ultra2 all new speeds are wide only.

SCSI Bus Termination

Each end of a SCSI bus must be terminated correctly. The ADIC Gateway
provides termination on each of its buses. The terminators can be disabled using
a jumper on the ADIC Gateway motherboard. They can also be enabled or
disabled from the ADIC Management Console. Each interface has a separate
control for the terminators.
Attention: Improper SCSI bus termination may result in excessive errors on the
SCSI bus, and may lead to data corruption or the inability to communicate with
target devices.
The ADIC Gateway provides termination power on all SCSI buses for external
terminators.
Many SCSI target devices have internal terminators. It is imperative that the
terminators be disabled for all devices EXCEPT those at the physical ends of the
SCSI bus.

Problems on the SCSI Bus

When A SCSI bus fails to operate correctly, it is most often caused by incorrect
connections to the SCSI bus. Common problems include:
42
• Missing terminator at the end of a SCSI bus: Check that an
external terminator is attached or that the end device has termi-
nation enabled.
• Excessive termination: Check that all devices other than the end
ADIC Gateway Setup