Digital logic electronics basics:

Electronic circuits can easily process signals that are in one of 2 conditions. Many well known digital integrated circuits (ICs) operate from a 5 volt power supply. Therefor, the input(s) of those ICs typically sense whether the voltage applied to them is near the negative side of the supply voltage of 0V (Low/0/Off/False) or the positive side of the supply voltage 5V (High/1/On/True). The output then, responds accordingly by outputting a high or low signal. How the output responds, depends on the circuitry connecting everything, which is categorized into different “logic gates”.

Commonly used terms for the 2 digital signal states:

  • High signal – On – 1 – True – (These terms are commonly used to indicate close to 5 volts)
  • Low signal – Off – 0 – False – (These terms are typically used to mean close to 0 volts)

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Basic logic gates:

  • NOT (only one input) – Output High, only if input is low.
  • AND – Output high, only if all inputs are high.
  • OR – Output High, if one or all inputs are high.
  • NAND – Output low, if all inputs are high.
  • NOR – Output low, if any inputs are high.
  • XOR – (2 inputs) Output high only when one input is high and the other input is low.
  • XNOR – (2 inputs) Output low only when one input is high and one input is low.

NAND = Not AND                   NOR = Not OR

XOR = Exclusive OR               XNOR = Exclusive NOR

Future topics:
  • Active low (low-true).
  • Boolean logic
  • Diode logic
  • TTL – transistor transistor logic – always 5V (3-5V high)
  • CMOS – Complimentary Metal Oxide Semiconductor
  • Assertion level logic
  • Open collector
  • ADCs – Analog to digital converters
  • DACs – Digital to analog converters


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