Scsi-Bus Conditions; Attention (Atn) - Tandberg Data SLR7-140 PROGRAMMER Manual

Tandberg Data
3.5.

SCSI-bus Conditions

3.5.1.

Attention (ATN)

The ATTENTION condition allows an Initiator to inform a
Target that the Initiator has a message ready. The Drive
may get this message by performing a MESSAGE-OUT phase.
The Initiator
asserting ATN at any time except during the ARBITRATION
or BUS FREE phases.
The Initiator
releasing ACK for the last byte transferred in a bus
phase for the ATTENTION condition to be honored before
transition to a new bus phase. An ATN asserted later
might not be honored until a later bus phase and then
may not result in the expected action.
The Initiator must keep ATN asserted if more than one
message byte is to be transferred.
The Initiator may negate the ATN signal at any time
except while the ACK signal is asserted during a MES-
SAGE-OUT phase.
while REQ is true and ACK is false during the last
REQ/ACK handshake of the MESSAGE-OUT phase.
If ATN occurs during a COMMAND phase, MESSAGE-OUT will
occur after transfer of all Command Descriptor Block
bytes has been completed.
If ATN occurs during
transferring parameters of a:
- INQUIRY
- LOG SELECT
- LOG SENSE
- MODE SELECT
- MODE SENSE
- READ BLOCK LIMITS
- READ POSITION
- RECEIVE DIAGNOSTIC RESULTS
- REQUEST SENSE
or
- SEND DIAGNOSTICS
command,
MESSAGE-OUT will occur after transfer of the complete
Parameter List.
3-12 Tandberg SLR Product Line SCSI Functional Specifications
creates the ATTENTION
must assert the
Normally, the
a DATA IN
Logical Characteristics
condition
ATN signal
Initiator negates
or OUT phase
by
before
ATN
while