Table 2.4 Synchronous Mode Data Transfer Request Setting - Fujitsu MBA3073 SERIES Technical Manual

The default data transfer mode between SCSI devices is asynchronous data transfer. The
asynchronous data transfer mode shall be selected when the power supply is turned on, a
TARGET RESET message is received, a RESET condition occurs, or a WIDE DATA
TRANSFER REQUEST message is received.
If the synchronous transfer mode has been selected between SCSI devices and if it is changed to
the asynchronous transfer mode for some reasons (such as the TARGET RESET message from
another INIT) that the remote SCSI device cannot detect, the local SCSI unit shall send the
SYNCHRONOUS DATA TRANSFER REQUEST message to select the transfer mode again or
exchange the message for mode change. Then, the local SCSI device shall start data transfer.
By considering the system performance affected by the message exchange overhead, avoid to
select the data transfer mode in every SELECTION sequence.
(5) Synchronous mode transfer function of HDD
a. Mode setup
When the TARG tries to control whether the HDD starts the negotiation if necessary, it can
specify using the CHANGE DEFINITION command.
Table 2.4
SDTR bit
Even if the HDD recognizes that the synchronous mode transfer and wide mode transfer
settings are necessary, the HDD does not send the SYNCHRONOUS DATA
"0"
TRANSFER REQUEST message. However, when the INIT sends the
SYNCHRONOUS DATA TRANSFER REQUEST message, the HDD responds to the
message correctly.
When the HDD recognizes that the synchronous mode transfer setting is necessary, the
"1" HDD sends the SYNCHRONOUS DATA TRANSFER REQUEST message after
completing the COMMAND phase.
Refer to Section 3.1.4 in SCSI Logical Specifications for details of setting method.
b. Transfer mode definition
(a) Default transfer mode
The default transfer mode is selected automatically when the power supply is turned on, a
RESET condition occurs, or the TARGET RESET message is received (initial state).
This mode is kept for each INIT individually. When an SCSI device executes the first
command, it exchanges the SYNCHRONOUS DATA TRANSFER REQUEST message
with others. If this message exchange is successful, the synchronous transfer mode is
selected between the two SCSI devices. If unsuccessful, the asynchronous transfer mode
is selected between them.
C141-C015
Synchronous mode data transfer request setting
Operation
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