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a. Transfer block count
When the "Transfer Data Length" field is specified as the "Number of Transfer Blocks",
this field specifies the number of logical data blocks transferred between the INIT and
IDD.
In a command with a 1-byte length, if the value specified in this field is zero, it is regarded
that 256 blocks have been specified, and specification in a range of from 1 to 256 blocks is
possible. On the other hand, in a command with a 2-byte length, when the value specified
in this field is zero, data transfer is not executed. Specification in a range of from 0 to
65,535 blocks is possible.
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 IDD 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 IDD, 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 IDD (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 IDD 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.
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