Rockwell Automation 1747-PT1, D1747NP002 Hand-Held Terminal - Manual (Page 421)

A–B
30 Chapter
30–1
Understanding Selectable Timed Interrupts –
SLC 5/02 Processor Only
This chapter applies to the SLC 5/02 processor only. It covers the following
topics:
•
STI operation
•
STI parameters
•
STD and STE instructions
•
STS instruction
•
INT instruction
The STI (selectable timed interrupt) function can be used with the SLC 5/02
processor only. This function allows you to interrupt the scan of the main
program file automatically, on a periodic basis, in order to scan a specified
subroutine file.
Basic Programming Procedure for the STI Function
To use the STI function with your main program file:
•
Create a subroutine file (range is from 3 to 255) and enter the desired
ladder rungs. This is your STI subroutine file.
Creating a subroutine file is discussed in chapter 7.
•
Enter the STI subroutine file number in word S:31 of the status file. (See
page 30–4.) A file number of zero disables the STI function.
•
Enter the setpoint (the time between successive interrupts) in word S:30
of the status file (see page 30–4). The range is 10 to 2550 milliseconds
(entered in 10ms increments). A setpoint of zero disables the STI
function.
Important: The setpoint value must be a longer time than the execution
time of the STI subroutine file, or a minor error (overrun bit
S:5/10) will occur.
After you download your program and enter the Run mode, the STI begins
operation as follows:
•
The STI timer begins timing.
•
At timeout, the main program scan is interrupted and the specified STI
subroutine file is scanned; simultaneously, the STI timer is reset.
•
When the STI subroutine scan is completed, scanning of the main
program file resumes at the point where it left off.
•
The cycle repeats.
STI Overview
Operation