scsi interface specification - Plasmon

SCSI COMMANDS AND STATUSCOMMAND IMPLEMENTATION REQUIREMENTSSCSI COMMANDS AND STATUSThis section defines the SCSI command and status structures, as they pertain to the LaserDrive, andprovides several examples.COMMAND IMPLEMENTATION REQUIREMENTSThe first byte of all SCSI commands contains an operation code as defined in this document. Three bits(bits 7 - 5) of the second byte of each SCSI command specify the logical unit if it is not specified using theIDENTIFY message. The last byte of all SCSI commands contains a control byte.RESERVEDReserved bits, fields, bytes and op codes are set aside for future use. A reserved bit, field or byte must beset to zero. A LaserDrive that receives a reserved bit, field or byte that is not zero, or receives a reservedop code, terminates the command with a CHECK CONDITION status and the Sense Key set to ILLEGALREQUEST.UNIT ATTENTION CONDITIONThe Unit Attention Condition is entered by the LaserDrive to report events of interest to Initiators. Theseevents include:• Successful completion of a spin up• BUS DEVICE RESET message• SCSI bus reset• Power on• Self reset (due to controller-detected error)• Change of vendor-unique mode select parameters• SEND DIAGNOSTIC command• LaserDrive executes selftestThe LaserDrive attempts to report a Unit Attention Condition by responding with a CHECK CONDITIONstatus to the next command with the exception of the INQUIRY and REQUEST SENSE commands.A Unit Attention Condition is pending for each Initiator until cleared by that Initiator. Clearing occursfollowing any command after a CHECK CONDITION status response (except INQUIRY and REQUESTSENSE).An Initiator determines that a Unit Attention Condition has occurred because a UNIT ATTENTION SenseKey is found in the sense data returned in response to the REQUEST SENSE command, and REQUESTSENSE.97653978 HPage 19