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7.5 Timing Rule
C156-E228-02EN 7-15
7.5 Timing Rule
Table 7.7 gives the timing required for operations on the SCSI bus.
Table 7.7 lists SCSI FAST-20 timing specifications for operations on the SCSI
bus. Table 7.8 lists asynchronous, SCSI-1, and FAST-SCSI timing specifications.
Table 7.7 Timing specifications (1 of 3)
No. Name Standard Timing specification
1 Arbitration Delay 2.4 µs min. The minimum wait period between the time the SCSI
device sends a BSY signal and the time the value on the
data bus for determining the priority of bus use is judged
in the ARBITRATION phase. A maximum time is not
defined.
2 Assertion Period 15 ns min. Minimum pulse width of an ACK signal sent by INIT
and an REQ signal sent by TARG for synchronous data
transfer.
3 Bus Clear Delay 800 ns max. Maximum allowable period between the time either of
the following events occurs and the time the SCSI
device stops driving all bus signals.
(1) Detection of the BUS FREE phase (when both
BSY and SEL signal become false during Bus
Settle Delay).
Note:
Maximum allowable period between the time both
BSY and SEL signal became false and the time the
bus is released is 1,200 ns.
An SCSI device that requires a period longer than
Bus Settle Delay for the detection of the BUS
FREE phase must release the bus within (Bus
Clear Delay) minus (Bus Settle Delay excess time).
(2) Another SCSI device asserts the SEL signal during
an ARBITRATION phase.
(3) The RST signal becomes true (RESET condition).
4 Bus Free Delay 800 ns min. Minimum wait period between the time the SCSI device
detects a BUS FREE phase and the time it sends a BSY
signal to initiate an ARBITRATION phase.
5 Bus Set Delay 1.8 µs max. Maximum allowable period between the time an SCSI
device detects a BUS FREE phase and the time it sends
BSY and SCSI ID signals to initiate an ARBITRATION
phase.