Appendix B. SCSI Bus Signal Timing
B–2 Quantum Atlas 10K II Ultra 160/m SCSI Hard Disk Drives
Table B–1 SCSI Bus Timing Values -- ANSI SCSI-2 Standard (continued)
Timing Description Value Description
Cable Skew Delay 10 ns Maximum difference in propagation time allowed
between any two SCSI bus signals measured
between any two SCSI devices.
Data Release Delay 400 ns Maximum time for an initiator to release the
DATA BUS signals following the transition of the
I/O signal from false to true.
Deskew Delay 45 ns Minimum time required to wait for all signals
(especially data signals) to stabilize at their
correct, final value after changing.
Disconnection Delay 200 µs Minimum time that a drive waits after releasing
BSY before participating in an ARBITRATION when
honoring a DISCONNECT message from the
initiator.
Hold Time 45 ns Minimum time added between the assertion of
REQ or ACK and changing the data lines to
provide hold time in the initiator or drive while
using standard (slow) synchronous data transfers.
Negation Period 90 ns Minimum time that a drive negates REQ while
using standard synchronous data transfers; also,
the minimum time than an initiator negates ACK
while using standard (slow) synchronous data
transfers
.
Power-On to 10 s
*
Recommended maximum time from power
Selection Time application until a drive is able to respond with
appropriate status and sense data to the TEST
UNIT READY, INQUIRY, and REQUEST SENSE
commands.
Reset to Selection Time 250 ms
*
Recommended maximum time after a hard RESET
condition until a drive is able to respond with
appropriate status and sense data to the TEST
UNIT READY, INQUIRY, and REQUEST SENSE
commands.
Reset Hold Time 25 µs Minimum time for which RST is asserted; there is
no maximum time.
Selection Abort Time 200 µs Maximum time that a drive (or initiator) takes
from its most recent detection of being selected
(or reselected) until asserting a BSY response.
Selection Time-Out Delay 250 ms
*
Recommended minimum time a SCSI device
should wait for a BSY response during SELECTION
or RESELECTION before starting the time-out
procedure.
Transfer Period Minimum time allowed between the leading
edges of successive REQ pulses and of successive
ACK pulses while using standard or fast
synchronous data transfers. The period range is
200 to 500 ns minimum, standard, or 100 to 500
ns minimum, fast-synchronous.
Note:
negotiated and
set during an SDTR
message.
* Recommended time (continued)
