Cautions On Use (Common) - Mitsubishi Electric MELSEC FX3U Programming Manual

FX /FX /FX Series Programmable Controllers
3G 3U 3UC
Programming Manual - Basic & Applied Instruction Edition

36.2.3 Cautions on use (common)

This section 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 the EI (FNC04) and DI (FNC05) instructions are programmed in an interrupt routine in FX
PLCs, up to two interrupts can be accepted.
Double interrupts are not available in FX
3. Operation when a timer is used [interrupt function]
Make sure that counting using a general timer is disabled, even a 1ms retentive type timer.
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 sure inputs do not overlap with each other.
When using SFC program (STL instruction), do not drive state relays S in SET or OUT instruction in an
interrupt program.
5. When using SFC program (STL instruction)
When using SFC programs (STL instruction), do not drive state relays S using SET or OUT instructions in an
interrupt program.
6. 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.
To turn OFF a device held in the ON status or for canceling such a timer or counter held in the reset status,
reset such a device or deactivate RST instruction respectively inside or outsite the 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
Step 0
I001
PLCs.
3G
X001
M8000
36 Interrupt Function and Pulse Catch Function
FNC 04
EI
K10
C0
FNC 06
FEND
RST C0
Y007
FNC 05
IRET
36.2 Common Items
31
32
33
/FX
3U 3UC
34
35
36
37
38
A
B
853