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2.1 Command Format
C141-C013 107
b. Transfer byte length or parameter list length
When the transfer data length is specified as the "Transfer Byte Length" or
"Parameter List Length", this field specifies the length of the data transferred
between the INIT and HDD by that command in number of bytes. When zero is
specified in this field, data transfer is not executed, except in cases where it is
particularly stipulated in the specifications for individual commands in Chapter 4.
In commands which send the parameters which are necessary for command
execution are sent from the INIT to the HDD, this field is called "Parameter
List Length" and specifies the total number of bytes of the parameter list sent
by the INIT.
On the other hand, with commands which receive information from the HDD
(REQUEST SENSE, INQUIRY, etc.), it is called "Transfer Byte Length" and
specifies the maximum number of bytes that can be received from the INIT
(the number of bytes in the area secured in the INIT for receiving
information). The HDD transfers either the number of effective bytes of
information specified by the command or the value specified in the "Transfer
Byte Length", whichever value has the smaller number of bytes.
(4) Control byte
Table 2.5 Control byte
Bit 7 6 5 4 3 2 1 0
0 0 0 0 0 0 0 0
a. Bits 7, 6 (vendor unique)
When any value other than "0" is specified for these bits, the HDD terminates
command processing with the CHECK CONDITION status.
b. Bit 0 (Link)
This HDD does not support Link, so this bit should be set on "0".
(5) Handling an illegal CDB
If there are errors in the contents of a CDB description (specification), or if there
is an error in the specification of a parameter transferred from the INIT in
accordance with a CDB specification, that command ends with the CHECK
CONDITION status. In the case of a command that changes data on the disk
medium, when there is an error in the CDB specification, the disk medium is not
changed by that command, but when there is an error in a parameter transferred in
a DATA frame, the contents of the disk medium in the area specified in that
command may be changed. Also, a DATA frame request may be executed after
receiving a DATA frame, but those data are not used.