NoteCareful host Target Mode software design is necessary to prevent ambiguity in thenotification process. If a CCB was just prepared but the MBO has not yet beensearched by the host adapter at the time the MBI entry is made to the host, thehost may choose to examine the MBI entry and not act on it, having already pro-vided the needed CCB. The host should also examine the entire MBI space to besure that a previously supplied CCB which should have been able to service the no-tification MBI entry was not already used for a previous operation that had beenposted by the host adapter but not yet serviced by the host. Proper care in host sys-tem design will prevent these overlapping operations from becoming a problem.Command Block DefinitionThe CCB specifies detailed information about a SCSI command. The format of a CCBis shown below. Each of the fields is separately explained following the table.Command Control Block FormatByte Description Value Meaning0 Command Control BlockOperation Code00h SCSI Initiator command01h Target Mode command02h SCSI Initiator command withScatter/Gather03h SCSI Initiator command,residual data length returned04h SCSI Initiator command withScatter/Gather, residual datalength returned81h Bus Device Reset1 Address and Direction Control Bits 7-5 CCB OP Code = 00, 02, 03, 04:SCSI Target IdCCB OP Code = 01: SCSIInitiator IdBit 4 Outbound data transfer, lengthis checked.Bit 3 Inbound data transfer, length ischecked.Bit 2-0 Logical Unit Number2 SCSI Command Length3 Request Sense AllocationLength/Disable Auto Sense4-6 Data Length (Byte 4 mostsignificant)adaptec AHA-1740A/1742A/17445-20
