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COMMAND After transferring part or all of the command descriptor
block bytes.
DATA At the drive’s earliest convenience (often on a logical
block boundary). The initiator continues REQ/ACK
handshakes until it detects the phase change.
STATUS After the status byte has been acknowledged by the
initiator.
MESSAGE IN Before it sends another message. This permits a
MESSAGE PARITY ERROR message from the initiator
to be associated with the appropriate message.
SELECTION1Immediately after that SELECTION phase.
RESELECTION2After the drive has sent its IDENTIFY message for that
RESELECTION phase.
1Before the initiator releases BSY, provided the initiator asserted ATN
2The initiator should only assert the ATN signal during a RESELECTION phase
to transmit a BUS DEVICE RESET or DISCONNECT message.
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The initiator keeps the ATN signal asserted if more than one byte is to be
transferred. The initiator can negate the ATN signal at any time, except it does not
negate the ATN signal while the ACK signal is asserted during a MESSAGE OUT
phase. Normally, the initiator negates the ATN signal while the REQ signal is true
and the ACK signal is false during the last REQ/ACK handshake of the
MESSAGE OUT phase.