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14
SCSI ID: A unique data bit (the SCSI ID) shall be driven by each actively arbitrating SCSI device: the other
seven data bits shall be released (i.e., not driven) by this SCSI device. The parity bit [DB(P), DB(P1)]
may be undriven or driven to the true state, but shall never be driven to the false state during this
phase.
I&T:
The signal shall be driven by the initiator, target, or both, as specified in the Selection phase and
Reselection phase.
Init:
If this signal is driven, it shall be driven only by the active initiator.
None:
The signal shall be released; that is, not be driven by any SCSI device. The bias circuitry of the bus
terminators pulls the signal to the false state.
Winner:
The signal shall be driven by the one SCSI device that wins arbitration.
Target:
If the signal is driven, it shall be driven only by the active target.
2.2.1
Arbitration delay (2.4 µs)
The minimum time a SCSI device shall wait from asserting BSY for arbitration until the Data Bus can be exam-
ined to see if arbitration has been won. There is no maximum time.
2.2.2
Assertion period (90 ns)
The minimum time that a target shall assert REQ while using synchronous data transfers. Also, the minimum
time that an initiator shall assert ACK while using synchronous data transfers.
2.2.3
Bus clear delay (800 ns)
The maximum time for a SCSI device to stop driving all bus signals after:
1. The Bus Free phase is detected (BSY and SEL both negated for a bus settle delay).
2. SEL is received from another SCSI device during the Arbitration phase.
3. The transition of RST to assertion.
Note.
For the first condition above, the maximum time for a SCSI device to clear the bus is 1200 ns from BSY
and SEL first becoming both negated. If a SCSI device requires more than a bus settle delay to detect
Bus Free phase, it shall clear the bus within a Bus Clear delay minus the excess time.
2.2.4
Bus free delay (800 ns)
The minimum time that a SCSI device shall wait from its detection of the Bus Free phase (BSY and SEL both
negated for a bus settle delay) until its assertion of BSY when going to the Arbitration phase.
2.2.5
Bus set delay (1.8 µs)
The maximum time for a SCSI device to assert BSY and its SCSI ID bit on the Data Bus after it detects Bus
Free phase (BSY and SEL both negated for a bus settle delay) for the purpose of entering the Arbitration
phase.
2.2.6
Bus settle delay (400 ns)
The time to wait for the bus to settle after changing certain control signals as specified in the protocol defini-
tions.
2.2.7
Cable skew delay (10 ns)
The maximum difference in propagation time allowed between any two SCSI bus signals when measured
between any two SCSI devices.
2.2.8
Data release delay (400 ns)
The maximum time for an initiator to release the Data Bus signals following the transition of the I/O signal from
negation to assertion.
SCSI Interface Product Manual, Rev. J
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