1. Introduction

Programmable Logic Devices (PLD) are programmable systems and are generally used in manufacturing automation to perform different control functions, according to the programs written in its memory, using low level languages of commands. There are following three types of PLDs are being employed in mechatronics systems.

1. Microprocessor

   It is a digital integrated circuit which carries out necessary digital functions to process the information obtained from measurement system.

2. Microcomputer

   It uses microprocessor as its central processing unit and contains all functions of a computer.

3. Programmable Logic Controller (PLC)

   It is used to control the operations of electro-mechanical devices especially in tough and hazardous industrial environments.

A typical programmable machine has basic three components as shown in Figure 3.1.1:

1. Processor, which processes the information collected from measurement system and takes logical decisions based on the information. Then it sends this information to actuators or output devices.
   
   
2. Memory, it stores
   1. the input data collected from sensors
      
      
   2. the programs to process the information and to take necessary decisions or actions. Program is a set of instructions written for the processor to perform a task. A group of programs is called software .
3. Input/output devices : these are used to communicate with the outside world/operator.

Figure 3.1.1 Components of a programmable logic device