Signal Bus Timing; Table 3–3 Scsi-2 Bus Signal Definitions - Quantum DLT 8000 Product Manual

SCSI Description
Signal
RST (reset)
SEL (select)

3.4.2 Signal Bus Timing

The ANSI SCSI-2 standard defines the SCSI bus timing values shown in Table 3–4.
Timing Description
Arbitration Delay
Assertion Period
Bus Clear Delay
Bus Free Delay
Bus Set Delay
3-8
Table 3–3 SCSI-2 Bus Signal Definitions (continued)
Definition
An OR-tied signal that initiates a RESET condition.
An OR-tied signal used by an initiator to select a target or by a
target to reselect an initiator.
Table 3–4 SCSI Bus Timing Values
Value Description
2.4 µs Minimum time a SCSI device waits from asserting BSY
for arbitration until the DATA BUS can be examined to
see if arbitration has been won; there is no maximum
time.
90 ns Minimum time a drive asserts REQ while using
synchronous data transfers; also, the minimum time that
an initiator asserts ACK while using synchronous data
transfers.
800 ns Maximum time for a SCSI device to stop driving all bus
signals after:
For condition 1, the maximum time for a SCSI device to
clear the bus is 1200 ns (1.2 s) from BSY and SEL first
becoming both false.
If a SCSI device requires more than a bus settle delay to
detect BUS FREE, it clears the bus within a bus clear
delay minus the excess time.
800 ns Maximum time a SCSI device waits from its detection of
BUS FREE until its assertion of BSY when going to
ARBITRATION.
1.8 µs Maximum time for a device to assert BSY and its SCSI ID
bit on the DATA BUS after it detects BUS FREE to enter
ARBITRATION.
Quantum DLT 8000 Tape System
1. BUS FREE is detected.
2. SEL is received from another SCSI device during
ARBITRATION.
3. Transition of RST to true.