This document provides an overview of programmable logic controllers (PLCs). It discusses that a PLC uses a programmable memory to store instructions to implement logic and control machines. A PLC consists of a central processing unit, memory, and input/output processing devices. The central processing unit contains an arithmetic logic unit and control unit to perform operations. Memory in a PLC includes random access memory to store the operating system and programs in use, and read only memory to store essential boot up instructions. Input/output processing devices provide an interface between the PLC and external devices like sensors and motors to input and output signals.

1. PLC
Presented by
NAME : S.ARUNKUMAR
YEAR : IV YEAR
DEPARTMENT : MECHANICAL ENGINEERING
COLLEGE : SUDHARASAN ENGG COLLEGE

2. WHAT IS PROGRAMMABLE LOGIC CONTROLLER ?
A programmable Logic Controller (PLC)is defined as a digital
electronic device that uses a programmable memory to store
instructions and to implement functions such as logic,
sequencing, timing, counting and arithmetic in order to control
machines and processes,

3. ARCHITECTURE OF A PLC :

4. A PLC CONSISTS OF,
(i) CPU (CENTRAL PROCESSING UNIT)
(ii) MEMORY
(iii) I/O PROCESSING DEVICES

5. (i) CENTRAL PROCESSING UNIT:
A central processing unit ,also called a central processor or main
processor ,is the electronic circutory within the computer that carries
out the instructions of a computer program by performing the basic
arithmetic ,logic, controlling ,and input/output operations specified by
the instructions.
• The arithmetic logic unit (ALU), which performs arithmetic
operations like addition and subtraction and logical operations like
AND, OR,NOT and EX-OR etc.
• The control unit (CU), which extracts instructions from memory and
decodes and executes them, calling on the ALU when necessary.

6. • The arithmetic logic unit (ALU), which performs arithmetic
operations like addition and subtraction and logical operations
like AND, OR,NOT and EX-OR etc.
• The control unit (CU), which
extracts instructions from memory and decodes
and executes them, calling on the ALU when necessary.

7. FUNCTIONS OF CPU :
It consists of
Fetch,
Decode,
Execute,
Store.

8. Fetch:
Each instruction is stored in memory and has its own
address. The processor takes this address number from the
program counter, which is responsible for tracking which
instructions the CPU should execute next.
Decode:
All programs to be executed are translated to into Assembly
instructions. Assembly code must be decoded into binary
instructions, which are understandable to your CPU. This step is
called decoding.

9. Execute:
While executing instructions the CPU can do one of three
things: Do calculations with its ALU, move data from one
memory location to another, or jump to a different address.
Store:
The CPU must give feedback after executing an
instruction, and the output data is written to the memo

10. BUSES :
A bus is defined as a set of physical connections which
can be shared by multiple hardware components in order to
communicate with one another .All computers have four
fundamental buses: Data buses ,Address buses, Control buses
and System buses .
1) DATA BUSES,
2) ADDRESS BUSES,
3) CONTROL BUSES,
4) SYSTEM BUSES

11. (ii) MEMORY
• Memory devices are where the program are started in the
controller or some groups of binary digits of 1s and 0s stored
in the form of bytes at individual locations identified by their
addressed.
• The functions of memory sectors to store the status of inputs
and outputs.
• The sectors to store systems informations such as scan time
,fault status ,fault codes and watchdog timers .

12. There are several memory elements in PLC systems :
1) RANDOM ACCESS MEMORY (RAM)
2) READ ONLY MEMORY (ROM)

13. 1) RANDOM ACCESS MEMORY :
RAM (Random Access Memory) is the hardware in a computing
device where the operating system (OS), application programs
and data in current use are kept so they can be quickly reached by
the device's processor .
2) READ ONLY MEMORY(ROM):
• It is a type of storage medium that permanently stores data on
personal computers (PCs) and other electronic devices.
• It contains the programming needed to start a PC, which is
essential for boot-up; it performs major input/output tasks and
holds programs or software instructions.

14. (iii) I/O PROCESSING DEVICES :
The input and output unit provides the interface between the
system and the outside world and allowing connections to be
made through input/output channels to input devices such as
sensors and output devices such as motor and solenoids.

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