Seagate Ultra 160 Manual De Usuario

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                                                   Parallel SCSI Interface Product Manual, Rev. A 

hold time after the assertion of the REQ signal. The target shall assert the REQ signal for a minimum of one 
transmit assertion period. The target may then negate the REQ signal and change or release the DB(7-
0,P_CRCA) or DB(15-0,P_CRCA,P1) signals. The initiator shall read the value on the DB(7-0,P_CRCA) or 
DB(15-0,P_CRCA,P1) signals within one receive hold time of the transition of the REQ signal to true. The 
SCSI initiator port shall then respond with an ACK assertion. 

If the I/O signal is false (i.e., transfer to the SCSI target port), the SCSI initiator port, after detecting a REQ 
assertion, shall first drive the DB(7-0,P_CRCA) or DB(15-0,P_CRCA,P1) signals to their values, delay at least 
one transmit setup time, then assert the ACK signal. The initiator shall hold the DB(7-0,P_CRCA) or DB(15-
0,P_CRCA,P1) signals valid for at least one transmit hold time after the assertion of the ACK signal. The initia-
tor shall assert the ACK signal for a minimum of one transmit assertion period. The SCSI initiator port may then 
negate the ACK signal and may change or release the DB(7-0,P_CRCA) or DB(15-0,P_CRCA,P1) signals. 
The target shall read the value of the DB(7-0,P_CRCA) or DB(15-0,P_CRCA,P1) signals within one receive 
hold time of the transition of the ACK signal to true.

When a DT data transfer agreement has been established the target shall only use the DT DATA IN phase and 
DT DATA OUT phase for data transfers.

During DT data transfers, data shall be clocked on both the assertion and negation of the REQ and ACK signal 
lines. References to REQ/ACK transitions in this section refer to either an assertion or a negation of the REQ 
or ACK signal.

The REQ/ACK offset specifies the maximum number of REQ transitions that shall be sent by the target in 
advance of the number of ACK transitions received from the initiator, establishing a pacing mechanism. If the 
number of REQ transitions exceeds the number of ACK transitions by the REQ/ACK offset, the target shall not 
transition the REQ signal until after the next ACK transition is received. For successful completion of the DT 
DATA phase the number of ACK and REQ transitions shall be equal and both REQ and ACK shall be negated.

For the timing requirements of the negotiated transfer period see Section 3.5.2.

When information unit transfer agreement has been established (see Section 4.3.12):

a. information units shall be transferred on the DT DATA OUT phase and the DT DATA IN phase, and
b. the information units’ embedded iuCRC shall be used to detect information unit data errors. 

If the I/O signal is true (i.e., transfer to the initiator), to transfer SPI information units, the target: 

1. shall drive the DB(15-0) signals to their values;
2. shall wait at least one transmit setup time from DB(15-0) being driven with valid data;
3. shall transition the REQ signal;
4. shall hold the DB(15-0) signals valid for a minimum of one transmit hold time;
5. may change or release the DB(15-0) signals; and
6. shall not change the REQ signal for a minimum of one transmit assertion period.

If the I/O signal is true (i.e., transfer to the initiator), to receive SPI information units, the initiator shall:

1. read the value on the DB(15-0) signals within one receive hold time of the transition of the REQ signal; 

and

2. respond with an ACK transition.

If the I/O signal is false (i.e., transfer to the target), to transfer SPI information units, the initiator: 

1. shall wait until after detecting a REQ transition;
2. shall drive the DB(15-0) signals to their desired values;