PROGRAMMABLE LOGIC
CONTROLLER
FUNDAMENTALS OF LOGIC…”

• PLC operates on the binary principle like all digital equipment.
• Term “binary principle”
 refer to the idea that many things can be thought of as existing in one of two states.
• states can be defined as “high” or “low” ,
“on” or “off” , “yes” or “no” , and “1” or “0” .
• This two-state binary concept, applied to gates, can be the basis for making decisions.

• Gate  device that has one or more inputs with which it will perform a logical decision and produce a result at its one output .
• Logic  ability to make decisions when one or more different factors must be taken into account before an action is taken.

Light Switch
High Beam Switch
AND
High Beam
Light
The automotive high beam light can only be turned on when the light switch AND high beam switch are on.

Binary 1 represents the presence of a signal or the occurrence of some event, while binary 0 represents the absence of the signal or nonoccurrence of the event.

‘AND’ GATE
APPLICATION…EXAMPLE 1
Basic Rules
The device has two or more inputs and one output
If any input is 0, the output will be 0
If all inputs are 1, the output will be
1

‘AND’ GATE
APPLICATION…EXAMPLE 2
The AND gate operates like a series circuit.
The light will be “on” only when both switch A and switch B are closed.

Passenger Door Switch
Driver Door Switch
Dome
Light
The automotive dome light will be turned on when the passenger door switch OR the driver door switch is activated.

An OR gate can have any number of inputs but only one output.
The OR gate output is 1 if one or more inputs are 1.

‘OR’ GATE
APPLICATION…EXAMPLE 1
Basic Rules
If all inputs are 0, the output will be 0
If one or more inputs are 1, the output will be 1

‘OR’ GATE
APPLICATION…Example 2
The OR gate operates like a parallel circuit.
The light will be “on” if switch A or switch B is closed.

The NOT function has only one input and one output.
The NOT output is 1 if the input is 0.
The NOT output is 0 if the input is 1.
Since the output is always the reverse of the input it is called an inverter.

‘NOT’ GATE APPLICATION – Example 1
Acts like a normally closed pushbutton in series with the output.
The light will be “on” if the pushbutton is not pressed.
The light will be “off” if the pushbutton is n pressed.

‘NOT’ GATE APPLICATION – Example 2
Low-pressure indicating circuit
If the power is “on”
(1) and the pressure switch is not closed
(0), the warning indicator will be “on”
When the pressure rises to close the pressure switch, the warning indicator will be switched "off"

NAND FUNCTION
Functions - like an AND gate with an
inverter connected to its output.
The only time the NAND gate output is 0 is when all inputs are binary 1.

NOR FUNCTION
Functions - like an OR gate with an
inverter connected to its output.
The only time the NAND gate output is 1 is when all inputs are binary 0.

XOR (EXCLUSIVE-OR) FUNCTION
Has two inputs and one output.
The output of this gate is HIGH only when one input or the other is HIGH, but not both.
Commonly used for comparison of two binary numbers.

A
B
GATE BOOLEAN EQUATIONS
Gate Boolean Equation
AND Y
Y = A B
A
B
OR
Y Y = A + B
A NOT Y
Y = A

BOOLEAN EQUATION – Example 1
Each logic function can be expressed in terms of a
Boolean expression

BOOLEAN EQUATION – Example 2
Any combination of control can be expressed in terms of a Boolean equation
AB
Y = AB + C
A + B
Y = (A + B) C

BOOLEAN EQUATION – Example 2
AB
Y = AB + C
A + B
Y = (A + B) C

Producing A Boolean Expression From A Given
Circuit – Example 1

Producing A Boolean Expression From A Given
Circuit – Example 2
Final equation: Y= AB + AB

Hard Wired versus Programmed Logic
The term hardwired logic refers to logic control functions that are determined by the way devices are interconnected.
Hardwired logic can be implemented using relays and relay ladder schematics.
Hardwired logic is fixed: it is changeable only by altering the way devices are connected.

Hard Wired versus Programmed Logic
Example 4-1

Hard Wired versus Programmed Logic
Example 4-2

Hard Wired versus Programmed Logic
Example 4-3

Hard Wired versus Programmed Logic
Example 4-4

Hard Wired versus Programmed Logic
Example 4-5

Hard Wired versus Programmed Logic
Example 4-6

Hard Wired versus Programmed Logic
Example 4-7

Hard Wired versus Programmed Logic
Example 4-8

Hard Wired versus Programmed Logic
Example 4-9