Bus Conditions; Attention Condition - Fujitsu MBA3073 SERIES Technical Manual

1.7

Bus Conditions

Two types of asynchronous control, the ATTENTION condition and RESET condition, shall be
defined to control or modify the bus phase transition sequence (bus conditions).
1.7.1

ATTENTION condition

The ATTENTION condition allows the INIT to report that the INIT has a message to be sent to
the TARG. The TARG receives the message from the INIT by starting the MESSAGE OUT
phase. Figure 1.41 shows the ATTENTION condition.
(1) Generation and release of ATTENTION condition (INIT)
The INIT can generate the ATTENTION condition by asserting the ATN signal except for the
ARBITRATION or BUS FREE phase.
When generating of an attention condition on the SELECTION phase following arbitration, the
INIT must set the ATN signal true at least System Deskew Delay × 2 before releasing the BSY
signal.
To create an attention condition during the SELECTION phase following a QAS, the SCSI
initiator port shall assert the ATN signal at least two system deskew delays before asserting the
INIT's ID on the bus.
When generating of a new ATTENTION condition in the INFORMATION TRANSFER phase,
to inform the TARG of the ATTENTION condition before the transition to the next new bus
phase or information unit, the INIT must set the ATN signal true before ATN transmit setup time
or more from the timing of setting false the ACK signal for the last byte being transferred in the
current bus phase or information unit. If the ATN sending timing is delayed, the TARG may not
be informed of the ATTENTION condition until the next bus phase or information unit. The INIT
may not operate as it should.
When transferring message information in several bytes in the MESSAGE OUT phase, the INIT
must keep the ATN signal true. The INIT can make the ATN signal false any time except while
the ACK signal is true in the MESSAGE OUT phase. When transferring the last byte in the
MESSAGE OUT phase, the INIT generally makes the ATN signal false during the period
between the time the REQ signal becomes true and the time it replies the ACK signal. In this case,
the INIT must set the ATN signal false before Deskew Delay × 2 or more form the timing of
setting true the ACK signal.
The INIT must make the ATN signal false before making the ACK signal true to transfer the last
message byte if so specified for the particular type of message to the TARG. (See Subsection 2.1.2.)
(2) Response against ATTENTION condition (TARG)
The TARG shall start the MESSAGE OUT phase and respond to the ATTENTION condition in
the following conditions. Also, the TARG shall enter the MESSAGE OUT phase when the ATN
signal is true after the TARG returns the MESSAGE REJECT or other message with halting the
MESSAGE OUT phase.
32 C141-C015