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The signal delay times for each bus phase are defined as follows-
No.
Item
1
Arbitration
delay
2
Assertion
period
3
Bus Clear
delay
4
Bus free delay
5
Bus set delay
6
Bus settle
delay
7
Cable skew
delay
8
Data release
delay
9
Deskew delay
10
Disconnection
Table 4-5
Signal delay times definition
Time
2.4 µs
The minimum time an SCSI device shall wait 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
The minimum time that a target shall assert REQ (or
REQB) while using synchronous data transfers. Also,
the minimum time that an initiator shall assert ACK
while using synchronous data transfers.
800 ns
The maximum time for an SCSI device to stop driving
all bus signals after: (1) The BUS FREE phase is
detected (BSY and SEL both false for a bus settle delay)
(2) SEL is received from another SCS] device during the
ARBITRATION phase (3) The transition of RST to true.
For the first condition listed. the maximum time for an
SCSI device to clear the bus is 1200 nanoseconds from
BSY and SEL first becoming both false. If an 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
800 ns
The minimum time that an SCSI device shall wait from
its detection of the BUS FREE phase (BSY and SEL
both false
1.8 _s
The maximum time for an SCSI device to assert BSY
and its SCSI ID bit on the DATA BUS after it detects
BUS FREE phase (BSY and SEL both false for a bus
settle delay) for the purpose of entering the
ARBITRATION phase
400 ns
The minimum time to wait for the bus to settle after
changing certain control signals as called out in the
protocol definitions
10 ns
The maximum difference in propagation time allowed
between any two SCSI bus signals measured between
any two SCSI devices.
400 ns
The maximum time for an initiator to release the DATA
BUS signals following the transition of the I/O signal
from false to true.
45 ns
The minimum time required for deskew of certain
signals
200 µs
The minimum time that a target shall wait after
releasing BSY before participating in an
ARBITRATION phase when honoring a DISCONNECT
message from the initiator
4-10
Definition
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