Fujitsu MBA3073 SERIES Technical Manual page 179

(b) Transfer mode establishment
The default transfer mode is released, and the synchronous transfer mode or the
asynchronous transfer mode is selected by the exchange of SYNCHRONOUS DATA
TRANSFER REQUEST message.
This mode is kept for each INIT individually and data transfer mode and synchronous
mode parameters of each INIT differ each other. Data is transferred in the transfer mode
selected between the INIT based on the SCSI ID of the INIT which is identified in the
SELECTION phase.
If the INIT is in this state, the HDD does not send the SYNCHRONOUS DATA
TRANSFER REQUEST message to request for reselection of the transfer mode or
changing the synchronous transfer mode parameters. However, if the INIT returns the
SYNCHRONOUS DATA TRANSFER REQUEST message again, the HDD responds to
it as described later and it selects the data transfer mode again or sets the synchronous
data transfer parameters again.
If the retry fails in the MESSAGE IN or MESSAGE OUT phase when the
SYNCHRONOUS DATA TRANSFER REQUEST message is exchanged, or if the
transfer mode selection sequence has failed, the transfer mode between the INIT moves
to the default transfer mode.
(c) Transfer mode when the SCSI ID is not defined for INITs
Even if the SCSI ID of the INIT is not posted in the SELECTION phase (if a single INIT
is used and if it does not use the RESELECTION phase), the message can be exchanged
and the data transfer mode can be selected between the HDD and the INIT. In this case,
the HDD sets a unique data transfer mode for the INIT which has the undefined SCSI ID.
If the system dynamically uses two types of SELECTION phase (where the SCSI ID of
the INIT is posted and it is not posted), the transfer mode must be selected for each data
transmission.
c. Transfer mode setup from INIT to HDD
Table 2.5 shows the HDD response to the first SYNCHRONOUS DATA TRANSFER
REQUEST message sent from the INIT. Also, this table lists the data transfer modes set
between the INIT and HDD by the response.
The INIT can send the SYNCHRONOUS DATA TRANSFER REQUEST message anytime.
However, the HDD shall send this message to the INIT for selection of synchronous data
transfer mode if the INIT has failed to send the SYNCHRONOUS DATA TRANSFER
REQUEST message by the end of COMMAND phase. It is required when the HDD still
maintains the default transfer mode to the INIT and when the synchronous transfer request is
enabled by the CHANGE DEFINITION command (see Paragraph "d").
172 C141-C015