Rockwell Automation 1747-PT1, D1747NP002 Hand-Held Terminal - Manual (Page 424)

Interrupts – 5/02 Processor Only
Chapter 30
Understanding Selectable Timed
30–4
The following parameters are associated with the STI function. These
parameters have status file addresses. They are described here and also in
chapter 27.
Word S:31 STI file number – This can be any number from 3 to
255. A value of zero disables the STI function. An invalid number
will generate fault 0023.
Word S:30 Setpoint – 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. (You enter a value of 1– 255, which results in a
10–2550 ms setpoint.) A value of zero disables the STI function. An
invalid time will generate fault 0024.
Bit S:2/0 Pending bit – Read only. This bit is set when the STI
timer has timed out while the STI file is either being scanned or is
disabled.
This bit will not be set if the STI timer expires while executing the
user fault routine.
This bit is reset upon the start of the STI routine, execution of an STS
instruction, powerup, and exit from the Run mode.
Bit S:2/1 Enable bit – 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/reset using the STE, STD, or STS
instruction, enable/disable takes effect immediately.
If this bit is set or reset by the user program or communications, it
will not take effect until the next end of scan.
Bit S:2/2 Executing bit – Read only. This bit is set when the STI
file is being scanned and cleared when the scan is completed. The bit
is also cleared on powerup and entry into the Run mode.
Bit S:5/10 Overrun bit – Read/write. This minor error bit is set
whenever the STI timer expires while the STI routine is executing or
disabled while the pending bit is set. When this occurs, the STI timer
continues to operate at the rate present in word S:30.
If the overrun bit becomes set, take the corrective action your
application dictates, then clear the bit.
STI Parameters