AH500 Programming Manual Symbol: Explanation: 1. When the value in the accumulative register turns from 1 to 0, the instruction PN keeps the value 1 in the accumulative register for a scan cycle. After the second scan cycle is finished, the value in the accumulative register changes to 0. 2. Please use the instruction FB_ PN in the function block. Example: Instruction: Operation: ： LD M0 Contact A of M0 is loaded. AND M1 Contact A of M1 is connected in series. PN The circuit is falling edge-triggered. OUT Y0.0 The coil Y0.0 is driven. Timing diagram: M0 M1 Y0.0 One scan cycle One scan cycle 5-22 Instruction code Operand Function PN - The circuit is falling edge-triggered.