Chapter 5 Basic Instructions Symbol Explanation 1. When the value in the accumulative register switches from 1 to 0, the PN instruction 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. Use the FB_ PN instruction in function blocks. Example Instruction Operation 5_ 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 M20 The coil M20 is driven. Timing diagram One scan cycle 5-19 Instruction code Operand Function PN - Triggering the circuit on the falling edge. M0 M 0 M1M 1 MY20 .00 One scan cycle On