Fujitsu MBA3073 SERIES Technical Manual page 185

If the TARG enters the MESSAGE IN phase and first sends the MESSAGE REJECT message to
the INIT immediately after the INIT has responded with the WIDE DATA TRANSFER
REQUEST message, such message exchange is made invalid and the two SCSI devices shall set
the 8-bit data bus width between them.
(4) Valid period of wide data transfer mode
After the exchange of WIDE DATA TRANSFER REQUEST message, the data bus width
determined between the two SCSI devices shall be kept valid until when:
•
TARGET RESET MESSAGE reception
•
RESET condition ("hardware RESET") occurrence
•
Transfer width change between the same SCSI devices
•
Power turned off
•
Change in the transceiver mode (e.g., LVD mode to SE mode).
The default data bus width is 8 bits between SCSI devices. The data bus width shall be initialized
to 8 bits when the power supply is turned on, a TARGET RESET message is received, or when a
RESET condition occurs.
(5) Wide mode transfer of HDD
a. Mode setting
When the HDD recognizes the wide mode data transfer to be set, the INIT can select whether
the HDD sends the WIDE DATA TRANSFER REQUEST message to the INIT by sending
the CHANGE DEFINITION command.
For details on setting, refer to Section 3.1.4 in the SCSI Logical Specifications.
b. Data bus width status determination
(a) Default 8-bit mode status
The default 8-bit data bus width mode is selected automatically when the power supply is
turned on, a RESET condition occurs, or the TARGET RESET message is received
(initial state). Each INIT has this default bus width mode. When the WIDE DATA
TRANSFER REQUEST message is first exchanged between SCSI devices, the 8-bit or
16-bit data bus width is set between them.
(b) Data bus width determination status
This status occurs when the default data transfer mode has been released and a data bus
width has been determined. This status can be set on each INIT, and the data bus width
of each INIT may differ.
Data is transferred within the data bus width set to 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 request for a change of data bus width. If its
change is requested by the INIT, the HDD shall respond to it and change the data bus width.
When changing the WIDE DATA TRANSFER REQUEST message, if the setting sequence
178 C141-C015