Basic Ladder Logic Instruction of a PLC

1. Bit Logic Instruction

• Normally Open (XIC)
• Normally Close (XIO)
• Positive Edge
• Negative Edge
• Output Energize (OTE)
• Output Latch (OTL)
• Output Unlatch (OTU)

2. Timer Logic Instruction

• Timer On Delay (TON)
• Timer Off Delay (TOF)
• Retentive Timer (RTO)

3. Counter Logic Instruction

• Count Up (CTU)
• Count Down (CTD)
• Count UP/Down (CTUD)

4. Comparison Logic Instruction

• Equal (EQU)
• Not Equal (NEQ)
• Greater Than (GRT)
• Greater Than or Equal (GEQ)
• Less Than (LES)
• Less Than or Equal (LEQ)
• Limit (LIM)

5. Arithmatic Logic Instruction

• Addition (ADD)
• Subtraction (SUB)
• Multiplication (MUL)
• Division (DIV)

6. Move Logic Instruction

• Move (MOV)
• Block Move (BKMV)
• Copy (COP)

Note :

✅ Various Types of Instruction Available In PLC.

✅ Other Instruction Use By Programmer as per Requirement.

Exclusive-NOR Gate Logic in PLC

PLC EXCLUSIVE-NOR Gate 

• We representing a Exclusive-NOR Logic Gate with two Inputs A and B.

  

  Exclusive-NOR Gate

Exclusive-NOR Gate Truth Table :

Inputs		Output
A	B
0	0	1
0	1	0
1	0	0
1	1	1

PLC Exclusive-NOR Logic :

• When Input A and Input B both are on then upper branch provide result output 1.
• When input A and Input B both are not activated then lower branch provide output 1.
• When Input A activated then output 0.
• When Input B activated then output 0.

PLC Exclusive-NOR Gate Logic

Exclusive-OR Gate Logic in PLC

PLC EXCLUSIVE-OR Gate 

• We representing a Exclusive-OR Logic Gate with two Inputs A and B.

  

  Exclusive-OR Gate

• Exclusive-OR Gate that gives output when either of the input is 1 but when both are 1.

Exclusive-OR Gate Truth Table :

Inputs		Output
A	B
0	0	0
0	1	1
1	0	1
1	1	0

PLC Exclusive-OR Logic :

• When Input A and Input B are not on then output 0.
• When input A is activated then upper branch provide result output 1.
• When input B is activated then lower branch provide result output 1.
• When both input A and Input B are activated there is no output.

  

  PLC Exclusive-OR Gate Logic

NOR Gate Logic in PLC

PLC NOR Gate

• We representing a NOR Logic Gate with two Inputs A and B.

NOR Gate

• NOR Gate provide same result is to put NOT gate on each Input and Follow with AND Gate for resulting inverted inputs.

NOR Gate Truth Table :

Inputs		Output
A	B
0	0	1
0	1	0
1	0	0
1	1	0

PLC NOR Logic :

• Ladder diagram starts with a normally close set of contact Input A and Input B with series with output.
• There is no input provide to Input A and Input B so contacts are closed an output on.
• There is Input provide to Input A and Input B so contacts open an output off.

  

  PLC NOR Gate Logic

Bit Logic Instruction Description

1. Normally Open (XIC)

• Normally Open contact work as a 0 state means energy flow cannot transfer so output off.
• When we provide Input and state change from 0 to 1 and output on.

Normally Open 

2. Normally Close (XIO)

• Normally Open contact work as a 1 state means energy flow transfer continuous output on.
• When we provide Input and state change from 1 to 0 and output off.

Normally Close

3. Positive Edge

• Positive Edge use for detect signal change state of 0 to 1.
• When it detect a change in the input signal from 0 to 1 energy flow transfer only of some time that signal change its state from 0 to 1.
• After energy flow can not transfer means when positive edge detect output on and off instantly.

Positive Edge

4. Negative Edge

• Negative Edge use for detect signal change state of 1 to 0.
• When it detect a change in the input signal from 1 to 0 energy flow transfer only of some time that signal change its state from 1 to 0.
• After energy flow can not transfer means when negative edge detect output on and off instantly.  

Negative Edge

5. Output Energize (OTE)

• Output Energize Instruction is an output coil. 
• Output Energize Coil state is depend on input state behavior.
• IF Input activate at that time output Coil energize on and Input not active at that time output coil energize off.

Output Energize

6. Output Latch (OTL)

• Output Latch instruction provide inbuilt latching function.
• When we provide power at Input side and Output Coil On and when we release power from input side and output coil remain on. 

Output Latch

7. Output Unlatch (OTU)

• Output Unlatch instruction provide inbuilt unlatching function.
• When we provide power at Input side and output coil off.
• This instruction use for deactivate output coil.

  

  Output Unlatch
  

  
  

NAND Gate Logic in PLC

PLC NAND Gate 

• We representing a NAND Logic Gate with two Inputs A and B.

  

  NAND Gate

• NAND Gate provide same result is to put NOT gate on each Input and Follow with OR Gate.

NAND Gate Truth Table :

Inputs		Output
A	B
0	0	1
0	1	1
1	0	1
1	1	0

 

PLC NAND Logic :

• When Input A AND B are both off is there an output on.
• When Input A AND B are both are not 1 is there an output on.

  

  PLC NAND Gate Logic

NOT Gate Logic in PLC

 PLC NOT Gate

• NOT Gate output on when Input Not Provide. And output off when Input Provide.

  

  NOT Gate

• NOT Logic gate Input A on Output must be off.
• NOT Logic gate Input A off Output must be on.

NOT Gate Truth Table :

Inputs	Output
A
0	0
0	0

 

PLC NOT Logic :

• Ladder diagram starts with a normally close set of contact Input A with series with output.
• There is no input provide to Input A so contacts are closed an output on.
• There is Input provide to Input A so contacts open an output off.

  

  PLC NOT Gate Logic

OR Gate Logic in PLC

PLC OR Gate

• We representing a OR Logic Gate with two Inputs A and B.

OR Gate

• OR Logic gate Input A OR Input B must be on for the Output.
• We use 1 to indicate an on signal and 0 to represent an off signal. So we consider output as 1 must have A OR B consider 1.

OR Gate Truth Table :

Inputs		Output
A	B
0	0	0
0	1	1
1	0	1
1	1	1

PLC OR Logic :

• Ladder diagram starts with a normally open set of contact Input A, to represent switch A and in parallel with normally open set of contact Input B, to represent switch B.
• Terminates with O represent the output. For output on both Input A OR Input B contacts have to be closed.

  

  PLC OR Gate Logic
  
  

AND Gate Logic in PLC

PLC AND Gate

• We representing a AND Logic Gate with two Inputs A and B.

  

  AND Gate Logic

• When A  AND B are both on is there an output on.
• We use 1 to indicate an on signal and 0 to represent an off signal. So we consider output as 1 must have A  AND B consider 1.

AND Gate Truth Table : 

Inputs		Output
A	B
0	0	0
0	1	0
1	0	0
1	1	1

PLC AND Logic :

• Ladder diagram starts with a normally open set of contact Input A, to represent switch A and in series with normally open set of contact Input B, to represent switch B.
• Terminates with O represent the output. For output on both Input A AND Input B contacts have to be closed.

  

  PLC AND Gate Logic