7DQGEHUJ'DWD 6&6,'HVFULSWLRQ
 7DQGEHUJ'/73URGXFW0DQXDO
 6&6,%XV&RQGLWLRQV
The SCSI bus has two asynchronous conditions: Attention and Reset.

 $WWHQWLRQ&RQGLWLRQ

The attention condition informs a drive that an initiator has a message ready. The
drive gets the message by performing a MESSAGE OUT phase. The attention
condition requires the following timing:
• The initiator creates the attention condition by asserting ATN at any
time except during the ARBITRATION or BUS FREE phases.
• The initiator negates the ATN signal at least two deskew delays before
asserting the ACK signal while transferring the last byte of the
message.
• If the drive detects that the initiator failed to meet this requirement,
then the drive goes to BUS FREE.
• Before transition to a new bus phase, the initiator asserts the ATN
signal, then waits at least two deskew delays before negating the ACK
signal for the last byte transferred in the current bus phase. Asserting
the ATN signal later cannot be honored until a later bus phase and
then cannot result in the expected action.
The drive responds with MESSAGE OUT as described in the following table.