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4-10
The signal delay times for each bus phase are defined as follows-
Table 4-5 Signal delay times definition
No. Item Time Definition
1 Arbitration
delay
2.4 æs 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.
2 Assertion
period
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.
3 Bus Clear
delay
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
4 Bus free delay 800 ns The minimum time that an SCSI device shall wait from
its detection of the BUS FREE phase (BSY and SEL
both false
5 Bus set delay 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
6 Bus settle
delay
400 ns The minimum time to wait for the bus to settle after
changing certain control signals as called out in the
protocol definitions
7 Cable skew
delay
10 ns The maximum difference in propagation time allowed
between any two SCSI bus signals measured between
any two SCSI devices.
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 false to true.
9 Deskew delay 45 ns The minimum time required for deskew of certain
signals
10 Disconnection 200 æs 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