Quantum 10K II - Manual (Page 357)

Appendix B. SCSI Bus Signal Timing
B–36 Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives
Table B–16 SYNCHRONOUS DATA TRANSFER REQUEST Message —
Field Descriptions
Field Description
Transfer Period Transfer periods are specified in 4-ns units (a transfer period value of 100
yields an actual transfer period of 400 ns (4 x 100)). The minimum
Transfer Period is 50 ns for ULTRA SCSI-3. The drive supports transfer
periods in the range from 50 to 400 ns in increments of 25 ns (that is 50,
75, 100...400). (The equivalent transfer period value (entries) for these
are 12, 18, 25...100, respectively.) The drive rounds up the initiator-
supplied transfer period that does not fall on one of these intervals
REQ/ACK Offset The drive supports a minimum offset value of 0. An offset value of zero
means that all data transfers are done asynchronously. The drive’s
maximum and default offset value is 31. If the initiator supplies an offset
value of less than 31 in its SYNCHRONOUS DATA TRANSFER REQUEST
message, the drive rounds down to the initiator’s value and echoes it in
its corresponding SYNCHRONOUS DATA TRANSFER REQUEST message;
otherwise, the drive returns a value of 31 as its synchronous data transfer
offset.
The drive performs asynchronous data transfers by default (after a hard
reset, the receipt of a SYNCHRONOUS DATA TRANSFER REQUEST
message exchange must occur before synchronous data transfers can
take place). The drive or the initiator can initiate the SYNCHRONOUS
DATA TRANSFER REQUEST message exchange based on the Initiate Sync
Negotiation (ISN) parameter For details, see section of this manual that
discusses the MODE SELECT commands “Quantum-Unique Page” (39h).
B.8.20 TARGET RESET Message (0Ch) (BUS DEVICE RESET)
The TARGET RESET message is sent from an initiator to direct the drive to clear all
tasks on the drive. Refer back to B.6.2, Reset Condition, for the steps taken during
this process.
The drive creates a Unit Attention condition for all initiators after accepting and
processing a TARGET RESET message. The additional sense code is set to TARGET
RESET OCCURRED.
B.8.21 TARGET TRANSFER DISABLE Message (13h)
The TARGET TRANSFER DISABLE message tells the drive that subsequent
reconnections for data transfer on the task must be performed by the initiator. The
target can connect for other purposes but cannot enter a DATA phase unless a
disconnection attempt is rejected.
When the drive is ready to transfer data for a disconnected task for which a TARGET
TRANSFER DISABLE message has been sent, the target reconnects to the initiator
for the task, sends a DISCONNECT message, and, if the initiator does not respond
with a MESSAGE REJECT message, goes to the BUS FREE phase.
B.8.22 TASK COMPLETE Message (00h) (COMMAND COMPLETE)
The TASK COMPLETE message is sent by the drive to an initiator to indicate that a
task has been completed and that valid status has been sent to the initiator. When