Elenco Understanding Logic Gates - Manual (Page 10)

U17
OR Gate
OR gates are used in digital logic circuits to perform a logical add. When one of the inputs is high (1), the
output is high. The output will only be low (0) when both inputs are low.
1
1
1
1
1
2
2 2 2
2
2
2
0
This circuit demonstrates how the OR Gate
(U17) works. Connect one end of the red
and black jumper wires to the A & B
inputs on U17 and the loose ends to either
low voltage (denoted as a “0”) or high
voltage (denoted as a “1”). If either input
A
OR input B are high (1, either green LED
is on), then the Q output on U17 will be
high (1), and the red LED (D1) will be on.
A
Q
B
The output of an OR gate is often
represented as the sum of the inputs, so
Q = A+B .
Input (A) Input (B) Output (Q)
0 0 0
0 1 1
1 0 1
1 1 1