Digital Equipment RW504-ZA, Service Manual

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Drive Log
This data indicates the number of times the autochanger uses the drive.
Runtime Log
An entry is put into this log each time an error occurs that requires any form
of recovery. Both ‘‘on-the-fly’’ and extensive recovery methods are logged. The
type of error, the method of recovery, and the number of moves to that point are
recorded.
Odometer
This value indicates the total number of moves executed since the nonvolatile
RAM was first initialized. Power-on hours are also recorded.
6.7 The SCSI Interface
As defined by ANSI (American National Standards Institute), SCSI allows up to
eight devices on the bus in any combination of computers and peripherals. The
devices can communicate with one another without control from a host computer.
Another powerful feature is the ability of SCSI to perform arbitration. SCSI
allows the host to initiate transactions, then break communication with a device,
do something else, and reestablish communication when the device is ready.
Finally, SCSI is capable of high data transfer rates. Synchronous data transfer
rates may be as fast as 4 Mbytes/second, and asynchronous rates up to 1.5
Mbytes/second, limited only by the capabilities of the computer and peripheral.
CAUTION
Do not switch off any peripheral on the SCSI bus without first checking
that the bus is not active.
Switching off can cause data loss, indeterminate bus states, or both.
6.7.1 SCSI Command Set
The following SCSI-2 commands can be used with the optical disk library.
Note
Detailed descriptions of these commands and their functionality with
optical products can be found in the following documents:
• American National Standards Institute (ANSI) document titled,
‘‘Small Computer System Interface - 2 (SCSI-2),’’ revision 10H
which is dated September, 1991. Copies of this publication can be
Theory of Operation 6–27