TANDBERG SLR7, Reference Manual, Page: 84 / 118

Tandberg Data Hardware Interface
___________________________________________________________________________
8-16 Tandberg SLR Reference Manual
8.5. Bus Conditions
The bus has two asynchronous conditions:
- Attention Condition
- Reset Condition
These conditions cause certain bus device actions and can alter the bus phase.
8.5.1. Attention Condition
The Attention Condition allows an Initiator to inform a Target that it has a message ready. The
Target may get this message by performing a Message Out Phase.
The Initiator creates the attention condition by asserting ATN at any time except during the
Arbitration or Bus Free Phases.
The Initiator must negate the ATN-signal at least two deskew delays before asserting ACK
while transferring the last byte of the message. An exception is the Identify Message which
may be followed by another Message Out.
The Initiator must assert ATN at least two deskew delays (90 ns) before negating the ACK-
signal for the last byte transferred in a Bus Phase for the Attention condition to be honored
before transition to a new Bus Phase. Asserting ATN later might not be honored until a later
Bus Phase and then may not result in the expected action.
The Drive will respond with Message Out Phase as follows:
a) If ATN becomes true during a Command Phase, the Target will enter Message Out
Phase after transferring all of the Command Descriptor Block bytes.
b) If ATN becomes true during a Data Phase, the Target will enter Message Out Phase at
the Target’s earliest convenience (see the SCSI functional specifications for details).
The Initiator will continue REQ/ACK handshakes until it detects the phase change.
c) If ATN becomes true during a Status Phase, the Target will enter Message Out Phase
after the Status Byte has been acknowledged by the Initiator.
d) If ATN becomes true during a Message In Phase, the Target will enter Message Out
Phase before it sends another message. This permits a Message Parity Error message
from the Initiator to be associated with the appropriate message.
e) If ATN becomes true during a Selection Phase and before the Initiator releases BSY, the
Target will enter Message Out Phase immediately after that Selection Phase.
f) If ATN becomes true during a Reselection Phase, the Target will enter Message Out
Phase after the Target has sent its Identify message for that Reselection Phase.