Chapter 5 Basic Instructions Symbol S ： For internal use Explanation 1. When the value in the accumulative register switches from 1 to 0, the FB_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. The previous state of the contact is stored in the bit device S . Do not use S repeatedly in the program. Otherwise, 5_ the wrong execution result appears. 3. Use FB_PN only in function blocks. Example Instruction Operation LD M0 Contact A of M0 is loaded. AND M1 Contact A of M1 is connected in series. FB_PN D0.0 The circuit is falling edge-triggered.
OUT M20 The coil M20 is driven. Timing diagram One scan cycle 5-21 Instruction code Operand Function FB PN _ S Triggering the circuit on the falling edge. Device DX DY X Y M SM S T C HC D S BOOL WORD DWORD LWORD UINT INT DINT LINT REAL LREAL TMR CNT STRING Data type S M0 M0 M1M1 M2Y00.0 One scan cycle On