Fujitsu MBA3073 SERIES Technical Manual page 85

Note:
1. The HDD supports up to 20 MHz (40 MHz on LVD) of synchronous data transfer (see
Table 1.7).
2. The default data transfer mode is asynchronous. When the power is first turned on, the
system is reset, or after the TARGET RESET message has been issued, data is
transferred in the asynchronous mode only. It continues until the synchronous transfer
mode is selected by the message exchange explained below.
(1) ST synchronous data transfer
The ST synchronous data transfer is available only when it has been defined between the INIT and
TARG by exchanging the SYNCHRONOUS DATA TRANSFER REQUEST or PARALLEL
PROTOCOL REQUEST message with each other. The following data transfer parameters are
determined and the possible transfer rates between the SCSI units are defined by this message
exchange.
•
REQ/ACK Offset: Number of REQ signals that the TARG can send before receiving the ACK
signal.
•
Transfer Period: Minimum repetition cycle of REQ and ACK signals.
The TARG can send multiple REQ signal pulses before receiving an ACK signal response if these
pulses do not exceed the limit specified by the REQ/ACK Offset parameter. When the difference
between the REQ and ACK signal pulses has reached this limit at the TARG, the TARG shall not
send a REQ pulse until it receives the leading edge of the next ACK pulse. The data transfer in
DATA phase can complete normally only when the REQ and ACK signal pulses become equal to
each other.
(a) The case of the I/O signal is true (transfer to the INIT)
1) The TARG first drives the DB(7-0,P_CRCA) or DB(15-0,P_CRCA,P1) signals to their
values.
2) The TARG waits at least one Transmit Setup Time.
3) The TARG asserts the REQ signal.
4) The DB(7-0,P_CRCA) or DB(15-0,P_CRCA,P1) signals are held valid for a minimum of
one Transmit Hold Time after the assertion of the REQ signal.
5) The TARG asserts the REQ signal for a minimum of one Transmit Assertion Period.
6) The TARG may then negate the REQ signal and change or release the DB(7-0,P_CRCA)
or DB(15-0,P_CRCA,P1) signals.
7) The INIT reads 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.
8) The INIT then responds with an ACK assertion.
(b) The case of the I/O signal is false (transfer to the TARG)
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