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SCSI PACKETS
7-2
7
Read/Write Packet
For common command set refer to Appendix A.
DISK. Commands sent to the controller are: Read ($28), and Write ($2A).
For a read or write function, the maximum number of bytes that can be
transferred in a single call is 16Mb. If you need more, the command must be
broken up into several calls. For controller type 13, the command control field
can turn on/off the cache within the drive. If the drive currently has cache in
the opposite state as the command control field cache bit, a mode select of page
38 is sent to the controller to turn on/off the cache prior to the read/write
command.
TAPE. Commands sent to the controller are: read ($08) and write ($0A).
A tape read or write operation starts at the current position and must be in the
correct mode (refer to the appropriate controller manual). To write, the
controller must be in general mode or write mode. General mode occurs after
a tape positioning command that does not read the tape data (space-to-end-of-
recorded-media). Also, the controller can be at Beginning Of Tape (BOT),
Table 7-2. SCSI Functions (cont’d)
SCSI
FUNCTION CODE DESCRIPTION
$4C Reserved
$50 Inquiry
$54 Load/Unload
$58 Recover Buffer Data
$5C Request Sense Data
$60 Check Status
$64 Reserve Device
$68 Release Device
$6C New Tape Attach
$70 New Read (disk and tape)
$74 New Write (disk and tape)
$78 New Disk Attach
$7C Open (read of first blocks of a device)