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9.5 Instruction of Leading Edge Detection Method
9.5.1 Instructions of Leading Edge Detection Method
Instructions using the leading edge detection operation
1. DF (leading edge differential) instructions
2. Count input for CT (counter) instructions
3. Count input for F118 (UDC up-down counter) instructions
4. Shift input for SR (shift register) instructions
5. Shift input for F119 (LRSR left-right shift register) instructions
6. NSTP (next step) instructions
7. Differential execution type high-level instruction (P13)
Leading edge detection method
• An instruction with a leading edge detection method operates only in the scan where its trigger
(execution condition) is detected switching from off to on.
(1) Standard operation
(2) Leading edge detection operation
How to perform leading edge detection
The condition of the previous execution and the condition of the current execution are compared, and the
instruction is executed only if the previous condition was off and the current condition is on. In any other
case, the instruction is not executed.
Precautions when using an instruction which performs leading edge detection
• When RUN begins, for example when the system is powered on, the off → on change of the execution
condition (trigger) is not detected. The instruction is not executed. Execution of the instruction will take
place as explained on the next page.
• When used with one of the instructions indicated in instructions 1 to 6 below which change the order of
execution of instructions, the operation of the instruction may change depending on input timing. Take
care regarding this point.
Be careful when using leading edge detection type instructions with control instructions, such
as:
1. MC and MCE instructions
2. JP and LBL instructions
3. LOOP and LBL instructions
4. CNDE instruction
5. Step ladder instructions
6. Subroutine instructions
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