Digital Signals
A digital circuit operates with only two process signals,
which are commonly referred to as "0" and "1".
But how do you generate these signals in digital electronics?
Look at the circuit diagram shown.
An arbitrary logical unit
has two inputs A
and B
and an output Q...
Circuit for a logic element with two inputs.
(Enlarge)
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Circuit diagram for a logic element with two inputs.
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You control the inputs with the
pushbutton switches S1 and S2...
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With open switches,
the resistors R1 and R2
ensure that 0V is applied to the inputs.
The logic unit interprets this as
A = 0 and
B = 0.
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If you press S1,
at the input A +9V is applied
and is interpreted as A = 1.
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If you press S2,
B = 1.
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The result Q is indicated by the
LED.
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If the result is Q = 0, the output is 0V. The LED is dark.
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If the result is Q = 1, the output is 9V. The LED lights up.
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Note...
Later the circuit diagrams show only the logic units,
without pushbutton switches and LEDs.
This offers a better overview.
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