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3.4 Maintenance, Diagnostic Commands
C141-E167
3 - 109
The “Transfer byte length” field in the CDB specifies the total number of bytes of header and buffer
data that can be received by the INIT. The IDD reads the data from the data buffer beginning from
the byte position in the data buffer specified in the “Buffer offset” field of the CDB and continuing
in order, then adds the 4-byte header to it and transfers it to the INIT. Data transfer is completed at
the point when the number of bytes of the header and data from the IDD’s data buffer, specified in
the “Transfer byte length” field, has been transferred, or at the point when transfer of the header and
all the data in the IDD’s data buffer, to the final byte position, has been completed. When zero is
specified in the “Transfer byte length” field, this command is terminated without executing a data
transfer.
The format and contents of the 4-byte header transferred in this mode are the same as in the case of
Mode = 0, 0, 0, 0. However, the “Effective buffer data length” field in the header indicates the size
(byte length) of the data from the byte position in the data buffer specified in the “Buffer offset”
field in the CDB to the final byte position in the data buffer, including that byte. Also, the length of
the buffer data transferred to the INIT by this command is the value for the number of bytes in the
[“Transfer byte length” field in the CDB – 4 bytes] or the value indicated in the “Effective buffer
data length” in the header, whichever is smaller.
(3) Mode = 0, 0, 1, 0: Data only, with address specification
The data transferred to the INIT when this mode is specified is only the data which the IDD reads
from the data buffer. The header is not transferred as it is in Mode = 0,0,0,0 and Mode = 0,0,0,1. In
this mode, address in the data buffer can be specified in the “Buffer offset” field in the CDB.
The “Transfer byte length” field in the CDB specifies the total number of bytes of buffer data that
can be received by the INIT. The IDD reads the data in order beginning from the byte position in
the data buffer specified in the “Buffer address” field and transfers it to the INIT. Data transfer is
completed at the point when the number of bytes of buffer data specified in the “Transfer byte
length” field has been completed or transfer of the buffer data to the final byte position of the IDD’s
data buffer is completed. When zero is specified in the “Transfer byte length” field, this command is
terminated without executing a data transfer.
(4) Mode = 0, 0, 1, 1: Buffer descriptor
When this mode is specified, the IDD transfers only the 4-byte buffer descriptor to the INIT. the
IDD’s data buffer attributes are indicated in the 4-byte buffer descriptor. Zero must be specified in
the “Buffer offset” field in the CDB when this mode is specified. The IDD transfers the data length
specified in the “Transfer byte length” field in the CDB or 4 bytes, whichever portion of data is
smaller, to the INIT. When zero is specified in the “Transfer byte length” field, this command is
terminated without executing a data transfer.
Bit
Byte
76543210
0 X’02’ Addressing Boundary
1 X’78’ Buffer Capacity (MSB)
2 X’00’ Buffer Capacity
3 X’00’ Buffer Capacity (LSB)
Figure 3.26 READ BUFFER command: buffer descriptor