34 Commands—Introduction
Fixed Bit Check
For the READ, VERIFY and WRITE commands, a Fixed bit set to 1 indicates that
the length parameter of the command is for fixed block mode. If fixed block
mode is selected then the block size in the Mode Select block descriptor must
not be zero. Otherwise
CHECK CONDITION is reported and the sense data is
set as described for the
ILLEGAL FIELD check.
Flag Link Check
This check ensures that the host has not set the Flag bit in the control byte of the
command without setting the Link bit as well. If the test fails then
CHECK
CONDITION
is reported with a sense key of ILLEGAL REQUEST and additional
sense of 2400h (invalid field in CDB). The Flag field is identified as the bad
field.
Illegal Command Check
If the drive does not recognize the opcode of the command that it has been
sent, it will do one of the following:
■ Report CHECK CONDITION status. The sense key will be set to ILLEGAL
REQUEST
and the additional sense code will be set to 2000h (invalid
command opcode).
■ Report an invalid field in the command descriptor block. The sense key will
be set to
ILLEGAL REQUEST, the additional sense code will be set to 2400h
(invalid field in CDB) and the field pointer in the sense data will be zero.
Illegal Field/Request Check
Checks are performed to ensure the host has not set any of the following in the
command descriptor block:
■ a fixed field
■ a reserved field
■ the control field
■ two or more fields to logically conflicting values
If a field has been set to an illegal value:
■ CHECK CONDITION status is reported to the host with a sense key of
ILLEGAL REQUEST and additional sense of 2400h “invalid field in CDB”.
