Quantum 10K II User Manual
Page 356
Appendix B. SCSI Bus Signal Timing
Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives
B–35
B.8.19 SYNCHRONOUS DATA TRANSFER REQUEST Message (01h)
The SYNCHRONOUS DATA TRANSFER REQUEST (SDTR) message exchange
establishes the permissible transfer period and the REQ/ACK offsets for the DATA
IN/DATA OUT phases. The transfer period is the minimum time allowed between
leading edges of successive REQ and ACK pulses. The REQ/ACK offset is the
maximum number of REQ pulses allowed to be outstanding before the leading edge
of its corresponding ACK pulse is received by the drive.
The agreement becomes invalid and reverts to asynchronous data transfer after any
condition that can leave the data transfer agreement in an indeterminate state such
as:
•
after a hard reset,
•
after a TARGET RESET message,
•
after a WIDE DATA TRANSFER REQUEST message, and
•
after a power cycle.
The format of the message fields are shown in Figure B-4 and described in Table b-
16.
Bit
7
6
5
4
3
2
1
0
Byte
0
Extended Message (01h)
(See Figure B–1)
1
Extended Message Length (03h)
2
SYNCHRONOUS DATA TRANSFER REQUEST code (01h)
3
Transfer Period
4
REQ/ACK Offset
Figure B–4 SYNCHRONOUS DATA TRANSFER-Data Format