Installation manual

Publication 1747-RM001G-EN-P - November 2008
11-12 Understanding Interrupt Routines
STI Parameters
The following parameters are associated with the STI function. These
parameters have status file addresses that are described here.
• STI file number (Word S:31) - This can be any number from 3 to 255. A
value of zero disables the STI function. An invalid number generates
fault 0023h.
• Setpoint (Word S:30) - This is the time between the starting point of
successive scans of the STI file. It can be any value from 10 to 2550
milliseconds. (For SLC 5/02 see page 11-8.) You enter a value of 1 to
255, which results in a 10 to 2550 ms setpoint. A value of zero disables
the STI function. An invalid time generates fault 0024h.
SLC 5/03 and higher processors: If S:2/10 is set, time is in 1 ms increments.
If this bit is clear, time is in 10 ms increments.
If the STI is initiated while in the REM Run mode by loading the status
registers, the interrupt starts timing from the end of the program scan in
which the status registers were loaded. If the STI has been previously
configured (with a different setpoint), the new setpoint takes effect only
after the previously-configured STI has timed out.
• STI Pending Bit (S:2/0) - This bit is set when the STI timer has timed
out and the STI routine is waiting to be executed. This bit is reset upon
starting the STI routine, execution of a true STS instruction, power-up,
or exit from the REM Run or Test mode.
SLC 5/02 specific: The STI pending bit is not set if the STI timer expires
while executing the fault routine.
SLC 5/03 and higher processors: This bit is set if the STI timer expires
while executing the DII subroutine or fault routine.
• STI Enable Bit (S:2/1) - The default value is 1 (set). When a file number
between 3 and 255 is present in word S:31 and a setpoint value between
1 and 255 is present in word S:30, a set enable bit allows scanning of the
STI file. If the bit is reset by an STD instruction, scanning of the STI file
no longer occurs. If the bit is set by an STE or STS instruction, scanning
is again allowed. The enable bit only enables/disables the scanning of
the STI subroutine. It does not affect the STI timer. The STS
instruction affects both the enable bit and the STI timer. The default
state is enabled. If this bit is set or reset using the STE, STD, or STS
instruction, enable/disable takes effect immediately. If this bit is set in
the user program using an instruction other than STE, STD, or STS, it
takes effect at the next end of scan.
SLC 5/02 specific: If this bit is set or reset by the user program or
communications, it does not take effect until the next end of scan.