Table of Contents
Advertisement
Figure 2–3
A SCSI chain: up to six (or
seven) devices can be linked
to the computer
Chapter 2 — Setting Up
Up to 6 or 7 linked SCSI devices, each with a unique ID
Computer: reserves SCSI ID #7 for a SCSI card
host adapter, or #0 and #7 if SCSI is built in
may cause data loss or electrical damage. Switch all devices off,
including the computer, before adding or removing SCSI devices.
2. Each SCSI device must have its own unique SCSI ID number.
No two SCSI devices can have the same SCSI ID number or
malfunctions may result. SCSI ID numbers are discussed later.
3. Total cable length should be less than 6 metres (20 feet).
The SCSI circuits can only transmit data reliably over short
lengths of cable. The total length of the chain is important,
including short lengths of cable inside the computer and other
SCSI devices. Internal cabling can be from 10 to 30 cm (4 inches to
1 foot), depending on the device.
4. The SCSI chain must be terminated correctly.
Failure to terminate the chain properly can result in intermittent
communication, no communication, or failure of the computer to
boot up. The correct way of terminating is discussed later.
5. Turn SCSI devices on and off in the right sequence.
Turn on all external SCSI devices before the computer: this
ensures that the SCSI bus is stable before your computer tries to
use it. Turn off the computer before turning off other devices. This
prevents external SCSI devices from 'hanging' the SCSI bus and
preventing further access. Never operate with some devices in a
chain turned off, as this degrades performance and signal quality.
6. Avoid mixing cable types, brands, and styles.
A common source of trouble is mixing poor-quality SCSI cables
with approved high-quality SCSI cables. Different cable types or
brands may have different types of construction, impedance, and
wire placement, and this can result in problems when they are
...
The last SCSI device
must be terminated
21
Advertisement
Table of Contents
