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FX
3U
/FX
3UC
Series Programmable Controllers
Programming Manual - Basic & Applied Instruction Edition
35 Interrupt Function and Pulse Catch Function
35.2 Common Items
35.2.3
Cautions on use (common)
This paragraph explains common cautions on using the interrupt function or pulse catch function.
Specific cautions on each interrupt function are explained in the description of each interrupt function.
1. Processing when many interrupts are generated
When many interrupts are generated in turn, priority is given to the first one. When many interrupts are
generated at the same time, priority is given to the one having the smallest pointer number.
While an interrupt routine is being executed, other interrupts are disabled.
2. When double interrupt (interrupt during another interrupt) is required [interrupt function]
Usually, interrupts are disabled in an interrupt routine (program).
When EI (FNC 04) and DI (FNC 05) instructions are programmed in an interrupt routine, up to two interrupts
can be accepted.
3. Operation when a timer is used [interrupt function]
Counting is disabled when a general timer is used. Even when a 1 ms retentive type timer is used, rigid
attention should be paid.
In an interrupt routine, use timers for routine program T192 to T199.
4. Non-overlap of input [input interrupt (with/without delay function) and pulse catch function]
The inputs X000 to X007 can be used for high speed counters, input interrupts, pulse catch, SPD, ZRN,
DSZR and DVIT instructions and for general-purpose inputs.
Make inputs do not overlap each other.
5. Operation of devices latched in the ON status [interrupt function]
Devices which were set to ON in an interrupt routine are held in the ON status even after the interrupt routine
is finished.
When RST instruction for a timer or counter is executed, the reset status of the timer or counter is also held.
For setting to OFF such a device held in the OFF status or for canceling such a timer or counter held in the
reset status, reset such a device or deactivate RST instruction inside or outside a routine.
Example in which outputs are latched
In the program example shown below, the counter C0 is provided to count X001. When X001 turns ON
from OFF, the interrupt program I001 is executed only in one scan, and then the counter C0 is reset and
Y007 is output.
1) Program example
M8000
K10
FNC 04
EI
C0
RST
C0
X001
FNC 06
FEND
FNC 05
IRET
I001
Y007
Step 0