Filter
Top Products
Command Processing
1 - 4 C141-E167
Furthermore, this field may be used with a different meaning, or it may not have any meaning at all,
depending on the type of command. There are also some commands which allocate 3 or more bytes
as the transfer data length field. Detailed specifications of these commands are described in the
individual command specifications in Chapter 3.
a. Transfer block count
When the “Transfer Data Length” is specified as the “Transfer Block Count,” this field specifies
the number of logical data blocks to be transferred between INIT and the IDD.
In commands where this field is 1 byte in length, if the field’s specified value is 0, it is regarded
as specifying 256 blocks, and it is possible to specify a block count ranging from 1 to 256 blocks.
On the other hand, in commands where this field is 2 bytes in length, if the field’s specified value
is 0, no data transfer is executed. It is possible to specify a block count ranging from 0 to 65,535
blocks.
b. Transfer byte length or parameter list length
When this field is specified as the “Transfer Byte Length” or “Parameter List Length,” that
command specifies data length to be transferred between the INIT and the IDD, expressed as the
number of bytes. When 0 is specified in this field, data transfer is not executed, except in cases
where it is expressly stated in the individual command specifications in Chapter 3.
In commands which send parameters necessary for executing a command from the INIT to the
IDD, this field is called the “Parameter List Length,” and it specifies the total number of types in
the parameter list which the INIT is sending.
On the other hand, in commands for receiving information from the IDD (REQUEST SENSE,
INQUIRY, etc.), this field is called the “Transfer Byte Length,” and specifies the maximum
number of bytes which the INIT can receive (the number of bytes of area secured within the
INIT for receiving information). The IDD transfers either the number of effective bytes of the
type of information specified in the command, or the value specified in the “Transfer Byte
Length” field, whichever is the smallest number of bytes, and only that number, to the INIT.
(5) Control byte
Bit 76543210
0000000Link
a. Link
Command link is specified by this bit is “1.” Details of the operation of the command link are
described in Section 1.3.2.
b. Bit 7, 6 (vendor unique)
Except in cases where it is expressly specified in the individual commands, specification of these
bits has no meaning, and the IDD disregards the specified values.