HP 220mx HP SureStore 9100mx Optical Disk Drive User's Guide - Page 63

Cable Lengths

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Operating This Drive on a SCSI Bus The SCSI Bus and This Drive Because a narrow device only has a 50-pin connector, it will 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 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 can't "see" the upper 8 data bits, that translates to it not being able to "see" wide devices with a SCSI ID above 8. Remember the host adapter is a device, so if you're mixing wide and narrow devices on the bus, your host adapter must be at an ID that all devices can address. If mixing narrow and wide devices is unavoidable, use the configuration described below: Operating the Drive on a SCSI Bus It is very important that the 68-pin to 50-pin cable is properly configured to assure that the eighteen truncated lines are properly terminated. Cable Lengths The drive can be mounted only on a single-ended SCSI bus. Because the drive is a "fast" SCSI device, the maximum bus length is 3 meters (9.8 feet). The internal cable length of the drive is .5 meters (1.6 feet) which leaves 2.5 meters (8.2 feet) for the rest of the bus. Appendix B B- 7

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Appendix B
B-7
Operating This Drive on a SCSI Bus
The SCSI Bus and This Drive
Operating the Drive
on a SCSI Bus
Because a narrow device only has a 50-pin connector, it will 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 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 can
’
t "see" the upper 8
data bits, that translates to it not being able to "see" wide devices with a SCSI ID
above 8. Remember the host adapter is a device, so if you
’
re mixing wide and
narrow devices on the bus, your host adapter must be at an ID that all devices can
address.
If mixing narrow and wide devices is unavoidable, use the configuration described
below:
It is very important that the 68-pin to 50-pin cable is properly configured to assure
that the eighteen truncated lines are properly terminated.
Cable Lengths
The drive can be mounted only on a single-ended SCSI bus. Because the drive is a
“
fast
”
SCSI device, the maximum bus length is 3 meters (9.8 feet). The internal
cable length of the drive is .5 meters (1.6 feet) which leaves 2.5 meters (8.2 feet) for
the rest of the bus.