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Chapter 7 SCSI Interface
WIDE DATA TRANSFER REQUEST
Perform negotiation of data width in data transfers.
Table 7.2.1.6 : WIDE DATA TRANSFER Message Format
Table 7.2.1.7 : WDTR message implied agreements
PARALLEL PROTOCOL REQUEST
Set the synchronous transfer, data width, and other data transfer options. The
autoloader does not return this message.
Table 7.2.1.8 : PARALLEL PROTOCOL Message Format
Bit
Byte
7
6
5
4
3
2
1
0
0
Extended Message(01h)
1
Extended Message Length(02h)
2
WIDE DATA TRANSFER REQUEST(03h)
3
TRANSFER WIDTH EXPONENT(m)
Responding SCSI device WDTR response
Implied agreement
TRANSFER WIDTH EXPONENT = 1
16-bit data transfer
TRANSFER WIDTH EXPONENT = 0
8-bit data transfer
MESSAGE REJECT message (as a result of the
responding message )
8-bit data transfer
Parity error (on responding message)
8-bit data transfer
Unexpected bus free (as a result of the responding
message)
8-bit data transfer
No response
8-bit data transfer
Bit
Byte
7
6
5
4
3
2
1
0
0
Extended Message(01h)
1
Extended Message Length(06h)
2
PARALLEL PROTOCOL REQUEST(04h)
3
TRANSFER PERIOD FACTOR
4
Reserved
5
REQ/ACK Offset
6
TRANSFER WIDTH EXPONENT(m)
7
Reserved
QAS_REQ DT_REQ
IU_REQ
