793
FX
3U
/FX
3UC
Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
35 Interrupt Function and Pulse Catch Function
35.5 Timer Interrupt (Interrupt in Constant Cycle)
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35.5
Timer Interrupt (Interrupt in Constant Cycle)
35.5.1
Timer interrupt (interrupt in constant cycle)
1. Outline
An interrupt routine is executed at every 1 to 99 ms without being affected by the operation cycle of a PLC.
2. Application
This type of interrupt is suitable when a certain program should be executed at high speed while the main
program operation time is long or when a program should be executed at a constant time interval in sequence
operations.
3. Basic program (programming procedure)
4. Number and operation of (three) timer interrupt pointers
An interrupt routine program is executed at every specified interrupt cycle time (1 to 99 ms). Use this type of
interrupt in control requiring cyclic interrupt processing without regard to the operation cycle of a PLC.
If the timer time is set to 9 ms or less, however, the timer interrupt processing may not be executed in an
accurate cycle in the following cases:
• When the interrupt program processing time is long
• When the main program contains an applied instruction whose processing time is long
*1.
Cleared when the PLC mode is changed from RUN to STOP.
Input number
Interrupt cycle (ms)
Interrupt disable
command
I6
An integer in the range from 1 to 99 is put in "
" in the pointer name.
Example: "I610" indicates a timer interrupt at every 10 ms.
M8056
*1
I7
M8057
*1
I8
M8058
*1
Step
0
I620
Interrupt
pointer
Interrupt
routine
Interrupts are
enabled
End of
main program
Main
program
When interrupt is
given at every 20 ms
Interrupt return
FNC 04
EI
FNC 06
FEND
FNC 03
IRET
END
Timer interrupts are enabled after EI instruction.
It is not necessary to program DI (disable
interrupt) if there is no zone where input
interrupts should be disabled.
FEND instruction indicates the end of the main
program.
Make sure to describe an interrupt routine after
FEND instruction.
The interrupt routine is executed at every 20 ms.
Create a program to be executed as interrupt.
IRET instruction returns the program execution
to the main program.
Main program
Interrupt subroutine
I
Timer time: 1 to 99 (ms)
Timer interrupt pointer (6, 7 or 8)