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CHAPTER 1 Command Processing
1.1 Command Format
1.2 Status Byte
1.3 Outline of Command Processing
1.4 Command Queuing Function
1.5 UNIT ATTENTION Condition
1.6 Sense Data Hold State
1.7 Command Processing Exceptions
1.8 Data Block Addressing
This chapter describes the basic logical specifications of the IDD command processing functions.
Note: The IDD operates as the target (TARG) on the SCSI bus. In the explanations in this chapter, the
IDD is mentioned as “TARG”, except in cases where a particularly clear distinction is necessary.
1.1 Command Format
Input/output operation commands from INIT (initiator) to the IDD are accomplished by the CDB
(Command Descriptor Block). The CDB is information transferred from INIT to TARG in the
COMMAND phase. In a number of commands, the parameters which are necessary for command
execution in the DATA OUT phase may be specified in addition to the CDB specification. Details
concerning these are described in the specifications for each individual command in Chapter 3.
The CDB used by the IDD has 3 formats, these formats have length of 6, 10 and 12 bytes.
The basic format of each respective CDB is shown in Figures 1.1, 1.2 and 1.3.
Bit
Byte
76543210
0 Operation Code
1 LUN Logical Block Address (MSB)
2 Logical Block Address
3 Logical Block Address (LSB)
4 Transfer Data Length
5 Control Byte
Figure 1.1 6-Byte CDB Basic Format