User's Guide

Page 30 DDS-4 SCSI Interface Manual, Rev. B
Move Medium Command
The SMC Move Medium command moves a cassette from one address to another
by specifying a Source Address and a Destination Address. Scorpion 240 requires
that one of the addresses be 1, the DTE (drive). This command cannot be used to
move a cassette from one magazine slot directly to another. However, when a
cassette is moved from the DTE, it is not required that it be placed back in the slot
from which it came; the Source Storage Element Address will then indicate the last
slot it occupied.
Exchange Medium Command
The SMC Exchange Medium command is used to swap the tape in the DTE for
another one. The command specifies a Source Address, First Destination Address,
and Second Destination Address. Scorpion 240 requires that the Source and
Second Destination addresses be storage elements (magazine slots) and the First
Destination Address must be the DTE. The command moves the cassette in the
DTE to the Second Destination Address and the cassette in the Source Address to
the DTE.
Both of the above commands check that there is a cassette in the source
address(es) and no cassette in the destination address before attempting to execute
the command. If an address is invalid or an element is inappropriately empty or full,
the autoloader mechanism will not move.
Furthermore, if one of the above commands is invoked with a cassette in the DTE,
all buffered data will be written to the tape and the tape positioned to PBOT before it
is removed.
Read Element Status Command
The current position of cassettes in the Autoloader can be obtained by a SCSI
initiator by issuing a Read Element Status command. During all movements of
cassettes inside the Autoloader, the previous storage element address of the
cassette in the magazine is tracked, making it unnecessary for this command ever
to scan the magazine or otherwise move the mechanism. This address is reported in
the Source Storage Element Address of the element descriptor; the address is valid
when the SVALID bit is one.
Initialize Element Status Command
The host computer can direct the Autoloader to scan its magazine by issuing an
Initialize Element Status command. If there is a cassette in the DTE, it will be
returned to its magazine slot before the scan begins, and it will remain in the slot
after the scan.