our software Ladder Diagram (LAD) Editor allows you to create programs similar to electronic circuit diagrams. Ladder diagram programming is a method chosen by many PLC programmers and maintenance personnel; It is an excellent language designed for new programmers. Basically, ladder diagram programs allow the CPU to simulate current from a power source, through a series of logical input conditions, and then enable logical output conditions. Logical decomposition into program segments. The program executes according to instructions, one program segment at a time, in order from left to right, and then from top to bottom. Once the CPU reaches the end of the program, it returns to the top of the program to restart.

图1 LAD editor

Various instructions are represented by graphical symbols, including three basic forms.

Graphic	Name	Description
	Input Contacts	Represents logical input conditions, used to simulate switches, buttons, internal conditions, etc. The normally open contact of the image is a type of input contact.
	output coil	Usually represents the logical output result, used to simulate lights, motor starters, intervention relays, internal output conditions, and other outputs.
	output command	Represents additional instructions, such as timers, counters, or mathematical instructions.

Box shaped output instructions cannot be concatenated,onlyFBD can concatenate output instructions.

1.1. key point