A typical CCB is shown below:Byte 0 Command Control Block Opcode+1 Tar/Init Data Out Data In LUN+2 SCSI Command Length = m+3 Returned Sense Info Length = n+4 Data Length (MSB, MID, LSB)+7 Data Pointer (MSB, MID, LSB)+10 Link Pointer (MSB, MID, LSB)+13 Command Link ID+14 Host Status+15 Target Status+16 Reserved+17 Reserved+18 SCSI Command Bytes (m Bytes)18 + m Allocated for Sense Data (n Bytes)Command Descriptor BlockThe Command Descriptor Block (CDB), a part of the Command Control Block, is astandard format command packet that is transmitted to the addressed SCSI device.It contains all the command information required by the SCSI device to perform thedesired operation. The Command Descriptor Block contains the command OperationCode followed by a Logical Unit Number (LUN), command parameters if required,and a control byte. A typical Group 0 6-byte CDB is shown below:Bit 7 6 5 4 3 2 1 0Byte 0 Operation Code1 LUN Logical Block Address (MSB)2 Logical Block Address3 Logical Block Address (LSB)4 Transfer Length5 Vendor Unique Reserved Flag LinkEISA-to-Fast SCSI Host Adapter Architecture2-7
