Execution Condition - Mitsubishi Electric MELSEC iQ-R Series Programming Manual

1.3

Execution Condition

Types of execution conditions
The following table lists the execution conditions of instructions.
Execution condition
On
Rising edge
Off
Falling edge

Every scan
*1 When the program is described in structured text language (ST) or function block diagram/ladder diagram (FBD/LD), EN will be the
precondition of the instruction.
Execution condition of each instruction
The execution condition varies depending on the instruction. For execution condition, refer to the details of each instruction in
this manual.
When the program is described in structured text language (ST) or function block diagram/ladder diagram (FBD/LD), EN will
be the execution condition. The instruction is executed only when EN is TRUE. The status of ENO will be the same as that of
EN.
Note that the execution condition of standard functions and function blocks differs depending on the existence of EN. If there
is no EN, the standard function or function block is executed at every scan. For the execution condition of the standard
function or function block with EN, refer to the details of each standard function or function block in this manual.
*1
Description
An instruction is executed during on. It is executed only while the precondition of the instruction is on. When the
precondition is off, the instruction is not executed.
An instruction is executed one time when turned on. It is executed only once on the rising edge (off to on) of the
precondition of the instruction and is no longer executed later even when the condition turns on.
An instruction is executed during off. It is executed only while the precondition of the instruction is off. When the
precondition is on, the instruction is not executed.
An instruction is executed one time when turned off. It is executed only once on the falling edge (on to off) of the
precondition of the instruction and is no longer executed later even when the condition turns off.
An instruction is always executed regardless of whether the precondition of the instruction is on or off. When the
precondition is off, the instruction performs off processing.
1 OVERVIEW
53
1.3 Execution Condition
1