3 Basic Instructions Program Example: Ladder diagram: Instruction code: Operation: X0 M0 LD X0 Loading in A contact of X0 LD M0 Loading in contact A of M0 SET Y0 Y0 latched (On) Timing Diagram: X0 M0 1 scan time Y0 Explanations: END instruction has to be placed in the end of a ladder diagram or instruction program. PLC will start to scan from address 0 to END instruction and return to address 0 to restart the scan. Explanations: NOP instruction does not conduct any operations in the program; therefore, after the execution of NOP, the existing logical operation result will be kept.
If you want to delete a certain instruction without altering the length of the program, you can use NOP instruction. Program Example: Ladder diagram: Instruction code: Operation:
NOP instruction will be omitted in the ladder diagram LD X0 Loading in B contact of X0 OUT Y1 Driving Y1 coil DVP-PLC Application Manual 3-16 PLF M0 PLF M0 M0 falling-edge output SET Y0 Mnemonic Function Program steps Controllers ES EX SS SA SX SC EH2 SV EH3 SV2 END Program End 1 N/A Operand Controllers ES EX SS SA SX SC E H2 SV EH3 SV 2 Mnemonic Function Program steps Controllers ES EX SS SA SX SC EH2 SV EH3 SV2 NOP No operation 1 N/A Operand Controllers ES EX SS SA SX SC EH 2 SV EH3 SV 2 NOP No operation 0 NOP Y1 NOP