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4.1.3.2
RESET CONDITION
The RESET condition, created by the assertion of RST,
is used to
immediately clear all devices from the bus and to reset these
devices and their associated equipment.
RESET can occur at any time and takes precedence over all other
phases and conditions.
Any device (whether active or not) can
invoke the RESET condition.
On RESET, all devices immediately
(within a BUS CLEAR DELAY,
800 nsec) deassert and passively
release all bus signals except RST itself.
The RESET condition stays on for at least one RESET HOLD TIME, 25
usee.
During the RESET condition, no bus signal except RST can
be assumed valid.
Regardless of the prior bus phase, the bus resets to a
BUS FREE
phase following a RESET condition.
By setting jumpers A-B on the ACB-5500 jumper header (J6), the
user can select either a hard reset mode or a soft reset mode.
When the jumper is installed, a hard reset mode is established.
When in hard reset mode, a RESET condition will force the ACB-
5500 to clear all uncompleted commands, to release all reserva-
tions including dual port reservations, and to return all other
modes,
including mode select, set limits, and diagnostic states
to their power on default conditions.
The next time a drive is
selected from the Initiator, the drive and all its mode select
parameters will be re-initialized.
When the jumper is not installed at position A-B, a soft reset
mode is established.
After clearing the SCSI bus information and
waiting until. the Reset Condition has ended, the ACB-5500 will
attempt to complete any uncompleted commands which were fully
identified.
All SCSI device reservations and operating modes are
preserved.
The ANSI X3T9.2 SCSI specification defines the condi-
tions under which commands are considered completely identified
and completed.
4.1.4
PHASE SEQUENCING
Phases are used on the bus in a prescribed sequence.
In all
systems,
the RESET condition can interrupt any phase and
is
always followed by the BUS FREE phase.
(Any other phase can also
be followed by the BUS FREE phase.)
The normal progression is from BUS FREE to ARBITRATION, from
ARBITRATION to SELECTION or RESELECTION and from SELECTION or
RESELECTION to one or more of the INFORMATION TRANSFER phases
(COMMAND, DATA, STATUS or MESSAGE).
500504-00
4-9
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