Appendix B. SCSI Bus Signal Timing
B–4Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives
B.2 SCSI-3 Bus Timing
SCSI devices that use a single transition (ST), i.e, they use only one edge of the
REQ/ACK signal to clock data, can provide data transfer rates of up to 80 MB per
second. Ultra 160/m SCSI-3, on the other hand, uses both edges of REQ/ACK, or
double transition (DT) to double the speed of the bus.
Table B-2 provides the timing values for SCSI bus controls defined by the SCSI-3
standard. Note that the QAS (Quick Arbritrate/Select) items are not supported by
the drive. Tables B–3 and B–4 provide SCSI bus data and information phase timing
values for ST and DT devices, respectively.
Table B–2 SCSI-3 Bus Control Timing
Description Values
Arbitration Delay 2.4 µs
Bus Clear Delay 800 ns
Bus Free Delay 800 ns
Bus Set Delay 1.6 µs
Bus Settle Delay 400 ns
Cable Skew (note 1) 4 ns
Data Release Delay 400 ns
DIFFSENS voltage filter time 100 ms
Physical Disconnection Delay 200 us
Power on to Selection (note 2) 10 s
QAS Arbitration Delay 1000 ns
QAS Assertion Delay 200 ns
QAS Release Delay 200 ns
QAS non-DATA phase REQ (ACK) period 50 ns
Reset Delay 200 ns
Reset Hold Time 25 µs
Reset to Selection (note 2) 250 ms
Selection Abort Time 200 µs
Selection Time-out Delay (note 2) 250 ms
System Deskew Delay 45 ns
Notes: 1 Cable Skew is measured at each device connection with
the transmitted skew subtracted from the received
skew.
2 This is a recommended time. It is not mandatory.