SCSI Interface Overview
Page
9
the library via the RS-422 interface. The Viper acts as a bridge, passing commands,
data, and status between the initiator and the library, as specified in the Library
Interface Encapsulated SCSI Protocol Manual.
In SCSI Medium Changer terminology, the library or autoloader appears as an
“independent medium changer,” because the tape drive and medium changer are at
different LUNs. Medium changer commands addressed to LUN 0 are rejected with
Check Condition and sense data of Illegal Request / Invalid Command Operation
Code (05/20/00).
Because of the relatively slow communication on the RS-422 interface, the Viper will
disconnect from the SCSI bus after receiving a command, after receiving data-out,
and after sending status. Data-in and status are sent to the initiator without
disconnecting between them.
If the link between the Viper and the library fails, a command will receive a status of
Check Condition and sense data of Aborted Command / Logical Unit Communication
Failure (0B/08/00).
If a SCSI bus reset is received, a target reset task management request is
transmitted to the library.
When command forwarding is disabled in mode page 22h, commands addressed to
LUN 1 will receive a status of Check Condition and sense data of Illegal Request /
Logical Unit Not Supported (05/25/00).
After Command Forwarding is enabled or disabled, the drive will respond to the next
command with a Check Condition and sense data of Unit Attention / Reported LUNs
Data Has Changed (06/3F/0E).
