The input voltages at A and B can be set either as high (a standard value) or low (0 V). Based on the combination of these inputs, the output voltage at C will be a definite value (high or low).
With the AND gate, if A and B are both high (represented by the number 1) then C will also be high. Otherwise C will be low (represented by the number 0).The following truth table for the AND gate is shown.
2 inputs
A B
1 output C
circuit symbol for AND gate
Input A 1
1 0
0 Table 24.1
OR Gate The diagram shows the circuit symbol for an OR gate.
With the OR gate, if either A or B are high then C will be high. Otherwise C will be low. The following truth table for the OR gate is shown.
Input A 1
1 0
0 Table 24.2
NOT gate The diagram shows the circuit symbol for a NOT gate. The NOT gate only has one input voltage. Using a transistor as a voltage inverter will allow it to operate as a NOT gate.
With the NOT gate, if A is high then C will be low. If A is low then C will be high. The following truth table for the NOT gate is shown.
