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CHAPTER 2 Command Processing 2.1 Command Format
2.2 Status Byte
2.3 Command Queuing Function
2.4 UNIT ATTENTION Condition
2.5 Sense Data Hold State
2.6 Power Condition
2.7 LED Display
2.8 Command Processing Exceptions
2.9 Data Block Addressing
In this chapter, the basic theory and specifications concerning HDD command
processing functions are described.
The HDD operates as the target (TARG). In the explanations given
in this chapter, the HDD is labeled "TARG", except in cases where
a particularly clear distinction is necessary.
2.1 Command Format
Input/Output commands from the INIT (Initiator) to the HDD are executed by the
CDB (Command Descriptor Block). The CDB is information which is transmitted
from the INIT to the TARG in the CMND frame. In a number of commands, other
than the CDB specifications, parameters which are necessary in executing a
command are specified in the DATA frame. Details concerning these commands
are described in the specifications for individual commands in Chapter 4.
The CDB used by the HDD has 4 formats, one with a length of 6, 10, 12 bytes and
the other with a length of 16 bytes. The basic format of each respective CDB is
shown in Tables 2.1, 2.2 and 2.3.