HP 220mx HP SureStore 220mx Optical Jukebox User's Guide - Page 88

Appendix B, The SCSI Bus and This Jukebox

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Operating This Jukebox on a SCSI Bus The SCSI Bus and This Jukebox Connecting devices of the same bus width, such as all narrow (50-pin) is a simple process of daisy-chaining the devices, and terminating both ends of the bus. Mixing narrow and wide devices invites problems. Mixing narrow and wide devices on a bus should be done only by a person experienced in SCSI configurations. Because wide (68-pin) buses need more data lines on the bus for data transfer, it's necessary for the cables connecting the devices to be 68 pin. Data would be lost if the devices were set up as depicted in the figure below. [1]Bus Adapter - connecting point for all SCSI devices [2] Wide SCSI Device - accepts IDs from 0 to 15 [3] 68-50-Pin SCSI Cable - adapts from wide to narrow connectors [4] Narrow SCSI Device - accepts IDs from 0 to 7 [5] Terminator - device on the ends of a SCSI bus to prevent reflected signals on the bus Because some narrow devices have only 50-pin connectors, they do not transmit the eight extra bits of data needed for the wide device on the end of the bus. Using only 50 lines also prevents the narrow device from passing along the IDs of devices at ID 8 or above. The lower eight data lines transfer commands and messages, allowing all devices, regardless of size, to co-exist on the bus. However, data transfers and device addressing occur on the higher bits. Since a narrow device B- 8 Appendix B

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B-8
Appendix B
Operating This Jukebox on a SCSI Bus
The SCSI Bus and This Jukebox
Connecting devices of the same bus width, such as all narrow (50-pin) is
a simple process of daisy-chaining the devices, and terminating both
ends of the bus.
Mixing narrow and wide devices invites problems. Mixing narrow and
wide devices on a bus should be done only by a person experienced in
SCSI configurations.
Because wide (68-pin) buses need more data lines on the bus for data
transfer, it
’
s necessary for the cables connecting the devices to be 68 pin.
Data would be lost if the devices were set up as depicted in the figure
below.
[1]Bus Adapter - connecting point for all SCSI devices
[2] Wide SCSI Device - accepts IDs from 0 to 15
[3] 68-50-Pin SCSI Cable - adapts from wide to narrow connectors
[4] Narrow SCSI Device - accepts IDs from 0 to 7
[5] Terminator - device on the ends of a SCSI bus to prevent reflected signals on
the bus
Because some narrow devices have only 50-pin connectors, they do not
transmit the eight extra bits of data needed for the wide device on the
end of the bus. Using only 50 lines also prevents the narrow device from
passing along the IDs of devices at ID 8 or above.
The lower eight data lines transfer commands and messages, allowing all
devices, regardless of size, to co-exist on the bus. However, data transfers
and device addressing occur on the higher bits. Since a narrow device