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SCSI Operating Registers
SYM53C825A/825AE Data Manual
5-23
Bit 6
SRST (Software Reset)
Setting this bit resets the SYM53C825A. All
operating registers are cleared to their respec-
tive default values and all SCSI signals are
deasserted. Setting this bit does not cause the
SCSI RST / signal to be asserted. T his reset will
not clear the 53C700 Compatibility bit or any
of the PCI configuration registers. T his bit is
not self-clearing; it must be cleared to clear the
reset condition (a hardware reset will also clear
this bit).
Bit 5
SIGP (Signal Process)
SIGP is a R/W bit that can be written at any
time, and polled and reset via CT EST 2. T he
SIGP bit can be used in various ways to pass a
flag to or from a running SCRIPT S instruc-
tion.
T he only SCRIPT S instruction directly
affected by the SIGP bit is Wait For Selection/
Reselection. Setting this bit causes that
instruction to jump to the alternate address
immediately. T he instructions at the alternate
jump address should check the status of SIGP
to determine the cause of the jump. T he SIGP
bit may be used at any time and is not
restricted to the wait for selection/ reselection
condition.
Bit 4
SE M (Semaphore)
T his bit can be set by the SCRIPT S processor
using a SCRIPT S register write instruction.
T he bit may also be set by an external proces-
sor while the SYM53C825A is executing a
SCRIPT S operation. T his bit enables the
SYM53C825A to notify an external processor
of a predefined condition while SCRIPT S are
running. T he external processor may also
notify the SYM53C825A of a predefined con-
dition and the SCRIPT S processor may take
action while SCRIPT S are executing.
Bit 3
CON (Connected)
T his bit is automatically set any time the
SYM53C825A is connected to the SCSI bus
as an initiator or as a target. It will be set after
successfully completing selection or when the
SYM53C825A has responded to a bus-initi-
ated selection or reselection. It will also be set
after the SYM53C825A wins arbitration when
operating in low level mode. When this bit is
clear, the SYM53C825A is not connected to
the SCSI bus.
Bit 2
INT F (Interrupt on the Fly)
T his bit is asserted by an INT FLY instruction
during SCRIPT S execution. SCRIPT S pro-
grams will not halt when the interrupt occurs.
T his bit can be used to notify a service routine,
running on the main processor while the
SCRIPT S processor is still executing a
SCRIPT S program. If this bit is set, when the
ISTAT register is read it will not automatically
be cleared. To clear this bit, it must be written
to a one. T he reset operation is self-clearing.
Note: If the INT F bit is set but SIP or DIP is not
set, do not attempt to read the other chip
status registers. An interrupt-on-the-fly
interrupt must be cleared before servicing
any other interrupts indicated by SIP or
DIP.
Note: T his bit must be written to one in order to
clear it after it has been set.