Basic Ladder Programming Instruction Categories

Most of the PLC brands have these four categories of instructions which are basic instructions, applied instructions, operation instructions and extended instructions. On this training, I will use the KEYENCE PLC instructions type for the explanation.
1. Basic instructions
These are the basic instructions used in making ladder programs. These instructions achieve control equivalent to general relay sequence circuits.
 Contact instructions
 Output instructions
 Timer instructions
 Counter instructions

2. Applied instructions
These instructions are used to control execution of ladder programs, modules, macros, etc. These instructions enable ladders to be programmed structurally.
 Index register instructions
 Shift register instructions
 Memory switch instructions
 Step instructions
 Flow instructions

3. Operation instructions
These instructions perform various compare, arithmetic and logic operations, and move/convert data. These instructions allow complex operation circuits to be programmed using few instructions.
 Data move instructions
 Arithmetic/compare instructions
 Logic operation instructions
 Data shift instructions
 Data convert instructions
 Text processing instructions

4. Extended instructions
These instructions use CPU internal functions and perform other complex processing simply.
 Data processing instructions
 Clock processing instructions
 Alarm instructions
 High-speed processing instructions