In general, the same coil can only appear once in a ladder diagram. If the same coil is used twice or more times in the program, it is called a "double coil output".
The number of times the address instruction PLC ladder logic diagram is used varies according to different instructions:
1. Four address instructions: 4 times to access, A1 operates A2, saves to A3, A4 is the address of the next instruction.
2. Three address instructions: access and save 4 times, remove A4, A1 operation A2, save to A3.
3. Two address instructions: access and save 4 times, remove A3, and the result is saved in A1 (destination operand), A2 is the source operand.