When switch “a” is closed (ON), input “A” is connected to ground, (0v) or logic level “0” (LOW) and likewise, when switch “b” is closed (ON), input “B” is also connected to ground, logic level “0” (LOW) and this is the correct condition we require. The two switches, “a” and “b”, represent the inputs to a generic logic gate.
So for example, if the two voltage levels are 0V and +5V, then the 0V represents a logic “0” and the +5V represents a logic “1”.įor example, consider the digital circuit on the left. These logic states are represented by two different voltage levels with any voltage below one level regarded as a logic “0”, and any voltage above another level regarded as logic “1”. But being digital, these circuits can only have one of two logic states, called the logic “0” state or the logic “1” state. We know that logic gates are the most basic building block of any digital logic circuit and that by using combinations of the three basic gates, the AND gate, the OR gate and NOT gate, we can construct quite complex combinational circuits. Modern digital logic gates, IC’s and micro-controllers contain many inputs, called “pins” as well as one or more outputs, and these inputs and outputs need to be correctly set, either HIGH or LOW for the digital circuit to function correctly. Digital logic gates can be used for connection to external circuits or devices but care must be taken to ensure that their inputs or outputs function correctly and provide the expected switching condition, and Pull-up Resistors do just that.
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