AP7500 Hardware Reference Guide
33
III.
Appendix
SCSI
Cable
Limits
III. Appendix
SCSI Cable Limits
SCSI cables have a limit to the length that it may have. Exceeding the length
may cause problems mounting or using any one of the SCSI devices.
CAUTION: Exceeding the SCSI cable limits may cause unreliable data
transfers even if all the devices are mounted properly.
NOTES:
•
Narrow refers to 50 pin and Wide refers to 68 pin. Don’t get confused by
the width of the connector or cable.
•
The SCSI ID for devices on one connector cannot be the same as the
SCSI ID for devices on the other connectors. None of the devices on any
connector can use ID7, which is reserved for the SCSI controller.
•
A maximum of 15 devices may be connected to the motherboard (three
connectors) at one time. The following “Max Devices” are for individual
connectors and do not take into account other SCSI devices.
Cable Limits
Max Data Transfer Rates
Max Devices
1) 12m (29.4ft)
Ultra2-SCSI (68 pin 80MB/Sec)
15
2) 3m - 1.5m
Wide Ultra-SCSI (68 pin 40MB/Sec)
4 - 8
3) 3m (9.8ft)
Wide-SCSI (68 pin 20MB/Sec)
15
4) 3m - 1.5m
Narrow Ultra-SCSI (50 pin 20MB/Sec) 4 - 7
5) 3m (9.8ft)
Narrow Fast-SCSI (50 pin 10MB/Sec)
7
Notes for the above chart:
1) A total of 15 “Ultra2-SCSI” devices (ID0-ID15) may be connected to the
68-pin Ultra2 connector on the motherboard.
NOTE: If connecting Fast/Ultra devices with Ultra2 devices on the Ul-
tra2 connector, the entire SCSI bus will be limited to the Ultra SCSI
conditions listed above. Mixing SCSI devices is highly not recommended.
2) A total of 8 “Wide Ultra-SCSI” devices (ID0-ID15) may be connected to
the 68-pin Wide connector if using a 1.5m (4.9ft) cable, but only 4 “Wide
Ultra-SCSI” devices if using a 3m (9.89ft) cable. Ultra-SCSI technology
is unstable over long lenghts, therefore stability will depend on they qual-
ity of your cable and devices.
3) A total of 15 “Wide-SCSI” devices (ID0-ID15) may be connected to the
68-pin Wide connector.
4) A total of 7 “Narrow Ultra-SCSI” devices (ID0-ID6) may be connected
to the 50-pin Narrow connector when using 1.5m (4.9ft) cable but only
4 devices when using 3m (9.8ft) cable. Ultra-SCSI technology is un-
stable over long lengths, therefore stability will depend on the quality of
your cable and devices.
5) A total of 7 “Narrow Fast SCSI” devices (ID0-ID7) may be connected to
the 50-pin Narrow connector.