Attention Condition - IBM Ultrastar 36LZX Specifications

10.3 Attention Condition

The attention condition allows an initiator to inform the drive that a MESSAGE OUT phase is desired.
The initiator may create the attention condition by asserting the ATN signal at any time except during the
ARBITRATION or BUS FREE phases.
The initiator must create the attention condition by asserting the ATN signal at least two deskew delays
before releasing ACK for the last byte transferred in a bus phase to guarantee that the attention condition
will be honored before transition to a new bus phase. This will guarantee a predictable drive response to
a message received during the MESSAGE OUT phase for this attention condition. If the ATN signal is
asserted later, it may be honored in the current bus phase or the next bus phase and then may not result
in the expected action.
After the initiator asserts the ATN signal, the drive will respond with the MESSAGE OUT phase as
follows:
Current Phase Response
COMMAND Message Out phase will occur after part or all of the Command Descriptor Block has
been transferred to the drive. The initiator must continue REQ/ACK handshakes
during the Command phase until the drive enters the MESSAGE OUT phase.
DATA The MESSAGE OUT phase will occur after part or all of the data bytes have been
transferred and not necessarily on a logical block boundary. The initiator must
continue REQ/ACK handshakes (asynchronous transfer) until it detects the phase
change.
Note: In synchronous transfer the initiator must continue sending ACK pulses to
reach an offset of zero.
STATUS The MESSAGE OUT phase will occur after the REQ/ACK handshake of the status
byte has been completed.
MESSAGE IN The MESSAGE OUT phase will occur before the drive sends another message.
SELECTION If ATN occurs during a SELECTION phase and before the initiator releases the BSY
signal, the MESSAGE OUT phase will occur immediately after that SELECTION
phase.
RESELECTION The MESSAGE OUT phase will occur after the drive has sent its IDENTIFY message
for that RESELECTION phase. (First the drive tries to complete the reselection.)
The initiator must keep the ATN signal asserted if more than one message byte is to be transferred dur-
ing the MESSAGE Out phase. The drive will process each message byte (multiple bytes for an extended
message) prior to receiving the next message from the initiator. The drive will continue to handshake
and process byte(s) in the MESSAGE OUT phase until ATN goes false unless one of the following
conditions occurs:
1. The drive receives an illegal or inappropriate message and goes to the MESSAGE IN phase to send
a MESSAGE REJECT message.
2. The drive detects a catastrophic error condition and goes to the BUS FREE phase.
Ultrastar 36LZX hard disk drive specifications
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