Scsi-2 Command Field Definitions - Spectra Logic Spectra 10000 User Manual

10kdev_.book Page 39 Friday, March 12, 1999 9:44 AM

SCSI-2 Command Field Definitions

Operation Code - (Byte 00, bits 7-0) The Operation Code of the command descriptor
block is a Group Code field and a Command Code field.
The three-bit Group Code field provides for eight groups of command codes. The
Operation Group Codes supported by the library are defined below:
The five-bit Command Code field provides for 32 Command Codes in each group. Thus,
a total of 256 possible Operation Codes exist. Specific Operation Codes are described in
detail in the sections for the individual SCSI commands.
Logical Unit Number - (Byte 01, bits 7-5) The Logical Unit Number for the library must
always be zero. The library's robotics controller is a single device target and does not
support multiple logical devices.
Reserved bits (Varies, See Specific Command) The reserved fields are set aside for future
standardization. Their use and interpretation may be specified by future extensions to the
SCSI-2 standard. All reserved bits, fields, or bytes will be set to 0, or as specified later in
any future extension to the SCSI-2 standard. If the library receives a reserved bit, field, or
byte that is not 0 or receives a reserved code value, it terminates the command with a
Check Condition status and the sense key is set to Illegal Request.
Command Descriptor Block Parameters (Varies, See Specific Command) The command
descriptor block (CDB) parameters contain fields which are defined in the specific
commands. These are used mainly for element addressing and parameter selection.
Bit 7 6 5
Byte
00
Group Code
Group Code Description
00h Six-byte commands
01h-02h Ten-byte commands
05h Twelve-byte commands
06h-07h Vendor-specific
4 3 2 1 0
Command Code