Synchronous Mode Data Transfer/Wide Mode Data Transfer - Fujitsu MAX3073NC - SCSI,80, Dell DC961,Hard Drive Scsi Logical Interface Specifications

3) After the INIT that accepts the IDENTIFY message normally completes the pointer restore
operation, it should make the ACK signal for the IDENTIFY message FALSE. If the
ATTENTION condition does not exist when the ACK signal becomes FALSE during
sending of the IDENTIFY message, the IDD regards the reconnection processing as having
been normally completed and begins subsequent processing.
For further details, refer to CHANGE DEFINITION parameter list (Reselection Retry,
Reselection Time-out Delay) in Section 3.1.4 and SCSI Bus (RESELECTION phase) in
Chapter 1 of "SCSI Physical Interface Specifications" and SCSI Bus Error Recovery
Processing in Chapter 3.
1.3.4

Synchronous mode data transfer/wide mode data transfer

The IDD equips a synchronous mode data transfer function and wide mode data transfer function for
processing high speed data transfers (DATA IN and DATA OUT phases) on the SCSI bus. Data
transfers on the SCSI bus can be executed in any desired combination of the asynchronous mode or
synchronous mode and in 8 bit widths or 16 bit widths (wide mode), but by using synchronous mode data
transfer or wide mode data transfer, command processing time is shortened and throughput for
input/output processing by multiple command processing using idle time on the SCSI bus can be
improved.
After IDD power on, after generating a RESET condition on the SCSI bus or after one of the INITs issues
a TARGET RESET message, the data transfer mode (default mode) of the IDD is the asynchronous
mode. To use wide mode data transfer, the INIT must exchange a WIDE DATA TRANSFER
REQUEST message or PARALLEL PROTOCOL REQUEST message with the IDD, and determine the
SCSI bus width.
SYNCHRONOUS DATA TRANSFER REQUEST message or PARALLEL PROTOCOL REQUEST
message and determine parameters necessary for executing the synchronous mode transfer. When
exchange of the WIDE DATA TRANSFER REQUEST message or PARALLEL PROTOCOL
REQUEST message is completed, if the synchronous mode has been established between the INIT and
IDD previously, note that the asynchronous mode is set.
The INIT which uses wide mode data transfer normally sends the WIDE DATA TRANSFER REQUEST
or PARALLEL PROTOCOL REQUEST message to the IDD following the IDENTIFY message after the
initial SELECTION phase, and requests the TARG (IDD) to set the SCSI bus width in the wide mode.
Also, if synchronous mode data transfer is used, after establishing the SCSI bus width, the INIT
exchanges the SYNCHRONOUS DATA TRANSFER REQUEST message or PARALLEL PROTOCOL
REQUEST message and requests the TARG (IDD) to set the synchronous data transfer mode.
The data transfer mode set with the INIT once is effective until a RESET condition occurs or until a
TARGET RESET message is issued by any INITs. Therefore, in order for the INIT to avoid overhead
time for message exchange, the INIT should not send the WIDE DATA TRANSFER REQUEST message
and the SYNCHRONOUS DATA TRANSFER REQUEST message or PARALLEL PROTOCOL
REQUEST message to the TARG each time the SELECTION phase is executed.
When the requesting synchronous mode transfer/wide mode data transfer by specifying of the CHANGE
DEFINITION command (synchronous mode transfer/wide mode data transfer request) is permitted, and
the IDD is maintaining the default transfer mode (asynchronous, 8-bit width), if a WIDE DATA
TRANSFER REQUEST message is not sent from the INIT, the IDD enters the MESSAGE IN phase
immediately after the COMMAND phase and sends the WIDE DATA TRANSFER REQUEST message
to the INIT for attempting to set the 16-bit width mode. After establishing the bus width, the IDD sends
the SYNCHRONOUS DATA TRANSFER REQUEST message to the INIT and attempts the
synchronous mode transfer parameters (REQ/ACK offset = 127, Transfer period = 25 ns).
C141-C010
To use the synchronous mode data transfer, the INIT must exchange the
1.3 Outline of Command Processing
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