The basic functions of a PLC depend on the control logic or programming technique used. Programming can be done using flowcharts or using ladder logic or using statement logic or mnemonics.
Putting all of this together, let’s see how we can write a program in the PLC.
First, the calculation flow chart. A flowchart is a symbolic representation of an instruction. This is the most basic and simple form of control logic, involving only logical decisions. The different symbols are as follows:
1. Write Boolean expressions of different logic. Boolean expressions typically involve logical operations such as AND, OR, NOT, NAND, and NOR. The different symbols are:
+ OR operator
. AND operator
! The NOT operator.
2. Write the description in a simple statement form:
IF input 1 AND input 2 then SET output 1 ELSE SET output.
Second, write ladder logic program. This is the most important part of PLC programming. Before explaining the programming of ladder logic, let us know some symbols and terms.
Rung: The step on the ladder is called a step. In short, the basic statement or a control logic is called Rung.
Y-normal output signal
M – motor symbol
T – timer
C – counter
Use the basic logic functions of ladder logic
3, write mnemonics: mnemonics are instructions written in symbolic form. They are also known as opcodes for handheld programming devices. The different symbols are as follows:
Ldi – load inversion
Ld – load
AND – and logic
OR – or logic
ANI – NAND and Logic
ORI – or non-logic
OUT – output