Command Phase; Data Phase; Status Phase (See Section 4.3) - Seagate ST11200 Product Manual

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If I/O is asserted (transfer to the initiator), the target shall first drive DB(7-0,P)* to their desired values, wait at
least one deskew delay plus one cable skew delay, then assert REQ. DB(7-0,P)* shall be held valid for a
minimum of one deskew delay plus one cable skew delay plus one hold time after the assertion of REQ. The
target shall assert REQ for a minimum of an assertion period. The target may then negate REQ and change
or release DB(7-0,P)*. The initiator shall read the value on DB(7-0,P)* within one hold time of the transition of
REQ to true. The initiator shall then respond with an ACK pulse.
If I/O is negated (transfer to the target), the initiator shall transfer one byte for each REQ pulse received. After
receiving a REQ pulse, the initiator shall first drive DB(7-0,P)* to their desired values, delay at least one
deskew delay plus one cable skew delay, then assert ACK. The initiator shall hold DB(7-0,P)* valid for at least
one deskew delay plus one cable skew delay plus one hold time after the assertion of ACK. The initiator shall
assert ACK for a minimum of an assertion period. The initiator may then negate ACK and may change or
release DB(7-0,P)*. The target shall read the value of DB(7-0,P)* within one hold time of the transition of ACK
to true.
3.1.6

Command phase

The Command phase allows the target to request command information from the initiator.
The target shall assert the C/D signal and negate the I/O and MSG signals during the REQ/ACK handshake(s)
of this phase.
3.1.7

Data phase

The Data phase is a term that encompasses both the Data In phase and the Data Out phase.
3.1.7.1 Data in phase
The Data In phase allows the target to request that it send data to the initiator.
The target shall assert the I/O signal and negate the C/D and MSG signals during the REQ/ACK handshake(s)
of this phase.
3.1.7.2 Data out phase
The Data Out phase allows the target to request that data be sent to it from the initiator.
The target shall negate the C/D, I/O, and MSG signals during the REQ/ACK handshake(s) of this phase.
3.1.8 Status phase
The Status phase allows the target to request that it send status information to the initiator.
See section 4.3 for details.
The target shall assert C/D and I/O and negate the MSG signal during the REQ/ACK handshake of this
phase.
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*And where applicable, DB(15-8, P1).
Product Manual - Disc Drive SCSI-2/SCSI-3 Interface (Vol. 2; Ver. 2), Rev. E