Cables and devices must be chosen to maximize performance and minimize the electrical noise from the
high-speed data transfers available with the SCSI protocol. Cabling and termination methods become
important considerations.
Exhibit 3.1-1 The following table lists the maximum number of devices you may connect at specific cable distances
using differential and single-ended SCSI in various SCSI environments.
SCSI-1
Fast SCSI
Fast Wide SCSI
Wide Ultra/WIDE SCSI
Wide Ultra/WIDE SCSI
Wide Ultra/WIDE SCSI
Ultra2 SCSI
Ultra160 SCSI
Ultra320 SCSI
Setting up cables and termination
Use high quality Ultra 320-rated, well-insulated
SCSI cables to ensure error free communications.
Exhibit 3.1-2 Several internal and external cable
connectors.
The ExpressPCI Ultra320 SCSI host adapter
supports two types of SCSI signaling: Low
7
ATTO Technology Inc. ExpressPCI Host Adapter Installation and Operation Manual
3.1 Cabling and termination
Bus speed
Bus width
MB/sec. max.
bits
5
8
10
8
20
16
40
16
40
16
40
16
80
16
160
16
320
16
Max. bus lengths, meters
Single-ended
LVD
6
-
3
-
3
-
-
-
1.5
-
3
-
-
12
-
12
-
12
Voltage Differential (LVD) and Single-Ended.
Devices on the same SCSI bus must use the same
signaling, either LVD or Single-Ended.
To set up cabling and termination:
1
Determine whether you are using a single
channel or dual channel host adapter model.
One external connector indicates a single
channel host adapter; two external connectors
indicate a dual channel host adapter.
2
Determine if SCSI devices are going to be
installed internally or externally.
• Total bus cable length varies by host adapter
and type of attached devices. Refer to
Exhibit 3.1-1 for details on maximum cable
length.
• If you combine Wide 16-bit and Narrow 8-
bit devices on the same connector, connect
the Wide devices first (closest to the
connector).
• Refer to the documentation for your SCSI
devices to determine if they are Wide or
Narrow, UltraWIDE SCSI, Ultra2 SCSI,
Ultra160 or Ultra 320.
3
Determine which terminator to use
Max. device
support
HVD
25
8
25
8
25
16
25
16
-
8
-
4
-
16
-
16
-
16
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