Basic logic gates - AND, OR, Inverter (NOT)
2-lnput AND gate (7409)
A
INPUT
B
OUTPUT
A AND B
0
0
0
0
1
0
1
0
0
1
1
1
Out = A AND B
Out = A.B
Out = A ∩ B
Experimental
Output
Output is 1 (True) if both input are 1 (true)
Output is 0 (False) if any of the input is 0 (False)
2-lnput OR gate
INPUT
Out = A OR B
Out = A+B
Out = A U B
OUTPUT
A
B
A OR B
0
0
0
0
1
1
1
0
1
1
1
1
Experimental
Output
Output is 0 (False) if both input are 0 (False)
Output is 1 (True) if any of the input is 1 (True)
Inverter (NOT) gate
Out = NOT A
Out = A’
Out =  A
INPUT
A
OUTPUT
NOT A
0
1
1
0
Experimental
Output
OTHER GATES
NAND gate (NOT AND)
INPUT
Out = NOT(A AND B) =  (A AND B) = (A AND B)’
Out = NOT (A.B) =  (A.B) = (A.B)’
Out = NOT (A ∩ B) =  (A ∩ B) = (A ∩ B)’
A
B
OUTPUT
NOT(A AND B)
0
0
1
0
1
1
1
0
1
1
1
0
NOR gate ( NOT OR)
INPUT
Out = NOT (A OR B) =  (A OR B) = (A OR B)’
Out = NOT (A+B) =  (A+B) = (A+B)’
Out = NOT (A U B) = (A U B) = (A U B)’
A
B
OUTPUT
NOT(A OR B)
0
0
1
0
1
0
1
0
0
1
1
0
Exclusive-OR gate (XOR)
INPUT
Out = A XOR B
Out = A ⊕ B
A
B
OUTPUT
A XOR B
0
0
0
0
1
1
1
0
1
1
1
0
Exclusive-NOR gate (NOT XOR)
Three Input Gates
http://www.kpsec.freeuk.com/gates.htm
Summary truth tables
Summary for all 2-input gates
Inputs
Summary for all 3-input gates
Inputs
Output of each gate
AND NAND
OR
A
B
C AND NAND OR NOR
1
0
0
0
0
1
0
1
1
0
0
0
1
0
1
1
0
0
1
0
0
1
0
0
1
1
0
0
0
1
0
1
1
0
1
1
0
1
0
0
0
1
1
0
1
0
1
0
1
1
0
1
1
0
0
1
1
0
1
1
1
1
0
1
0
A
B
0
0
0
1
0
1
0
0
1
0
1
1
0
1
0
0
1
1
1
1
1
0
1
Note that EX-OR and EX-NOR
gates can only have 2 inputs.
Output of each gate
NOR EX-OR
EX-NOR
For N number of inputs the total number of input combination will be: 2N
Example :
for 3 input the total combination is 23 = 8
for 2 input the total combination is 22 = 4
Combinations of logic gates
Logic gates can be combined to produce more complex functions.
For example to produce an output Q which is true only when input A is true and input B is false, as shown in the truth table
on the right, we can combine a NOT gate and an AND gate like this:
Input A
Q = A AND NOT B
Input B
Output Q
0
0
0
0
1
0
1
0
1
1
1
0
Working out the function of a combination of gates
Truth tables can be used to work out the function of a combination of gates.
For example the truth table on the right show the intermediate outputs D and E as well as the final output Q for the system
shown below.
Inputs
D = NOT (A OR B)
E = B AND C
Q = D OR E = (NOT (A OR B)) OR (B AND C)
Outputs
A
B
C
D
E
Q
0
0
0
1
0
1
0
0
1
1
0
1
0
1
0
0
0
0
0
1
1
0
1
1
1
0
0
0
0
0
1
0
1
0
0
0
1
1
0
0
0
0
1
1
1
0
1
1
Logic gates may be used for systems where the input/output signals can be described as one of the two states.
Pin configurations of IC's used In this experiment
A visual indication of the logic state or either an input or output signal can be provided by the light emitting diodes (LED's) in
the upper left hand corner of the Logic Trainer. If a LOGIC 1 state is present (+5 volts) then the LED will be lighted. If a
LOGIC 0 state is present (0 volts) and the LED will not be lighted.
The DATA SWITCHES on the Logic Trainer should be used to provide inputs to the logic devices/circuits.
Connected points