Seagate Ultra 320 ユーザーズマニュアル

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                                                   Parallel SCSI Interface Product Manual, Rev. A 

The above requirements in steps 6), 10), and 14) to not wait for the ACK transition corresponding to 
the previous REQ transition were not present in the SPI-3 standard. For compatibility with old designs 
SCSI initiator ports should generate ACK transitions for all received REQ transitions.

If the SCSI target port determines that a pad field is not required, has completed the data field transfer of the 
current data group, the I/O signal is true (i.e., transfer to the SCSI initiator port), and the REQ signal is negated, 
the SCSI target port shall:

1. wait at least one pCRC transmit hold time since the last REQ negation to assert P_CRCA;
2. wait at least one transmit hold time since the last REQ negation to assert the DB(15-0) signals to their 

pCRC values;

3. wait at least the longer of one pCRC transmit setup time from the assertion of P_CRCA or a transmit 

setup time from DB(15-0) being driven with valid pCRC data;

4. wait until the initiator has responded with all ACK transitions for the previous data group;
5. wait at least one transmit REQ negation period with P_CRCA transitioning since the last REQ nega-

tion;

6. assert the REQ signal;
7. hold the DB(15-0) signals for a minimum of one transmit hold time and hold the REQ signal asserted 

for a minimum of one transmit assertion period;

8. drive the DB(15-0) signals to their pCRC values;
9. wait at least one transmit setup time;
10.negate the REQ signal;
11. hold the DB(15-0) signals for a minimum of one transmit hold time and hold the P_CRCA signal 

asserted for a minimum of one pCRC transmit hold time; and

12.hold the REQ signal negated for at least one transmit REQ negation period with P_CRCA transitioning 

since the last REQ negation.

After either of the above sequences is complete, the target has ended a data group transfer. 

The initiator shall read the value on the DB(15-0) signals within one receive hold time of the transition of the 
REQ signal. The initiator shall then respond with an ACK transition.

The initiator shall continue to use the pad bytes, if any, for checking against the computed pCRC for the current 
data group. Upon receipt of the last byte of the pCRC field, the received pCRC and computed pCRC shall be 
compared. If they do match (i.e., no pCRC error), then the initiator shall negate the ACK signal. 

If received pCRC and computed pCRC do not match (i.e., a pCRC error is detected) or if an improperly format-
ted data group is transferred, then the initiator shall create an attention condition on or before the last transfer 
of the data group. When the target switches to a MESSAGE OUT phase, the initiator should send a SCSI initi-
ator port Detected Error message (see Section 4.3.5) to the target. This message notifies the target that data 
contained within the data group was invalid.

If the target does not retry transferring the information transfer or it exhausts its retry limit, the target shall go 
into a STATUS phase and send a CHECK CONDITION status with a sense key set to Aborted Command and 
an additional sense code set to Initiator Detected Error Message Received for the task associated with the 
received INITIATOR DETECTED ERROR message.

If the I/O signal is false (i.e., transfer to the target), the initiator determines the data field. Transfer to the target 
is completed by detecting an assertion of the P_CRCA signal. If the REQ signal is asserted (i.e., pad field 
required), the initiator shall first transfer the two pad bytes, then the four pCRC bytes. If the REQ signal is 
negated (i.e., no pad field required), the initiator shall transfer the four pCRC bytes.