Understanding Basic Logic Functions
Logic chips are integrated circuits designed to perform essential logic operations like AND, OR, XOR, NAND and NOR. While more advanced microcontrollers have replaced them in many modern devices, logic ICs were once fundamental building blocks of electronics.
In the past, before the era of microcontrollers, logic chips represented core components enabling complex circuits. They facilitated critical systems on early space missions as well, powering technologies aboard Gemini spacecraft and the Space Shuttle.
Though microcontrollers dominate today, some DIY projects may do just fine with basic logic chips. For circuits where a microcontroller would provide overkill, a simple logic IC could yield a sleeker, lower-power solution.
Rather than always opting for the latest technology, it pays to consider the right component for each unique application. Simple can suffice - and sometimes even shine - when complexity introduces unwanted bulk and energy use.
Making Sense of 1s and 0s: Common Digital Logic Types
In the world of circuits, logic is expressed through binary values like 1s and 0s or high/low states. Below are some fundamental logic types with their symbols and "truth tables" showing output conditions:
- AND Gate: Requires both inputs to be high for a high output.
- OR Gate: Outputs high if one or more inputs are high.
- NOT Gate: Inverts ("flips") the input - 1 becomes 0 and vice versa.
- NAND Gate: Produces a low output only if all inputs are high.
- NOR Gate: Outputs low only if all inputs are low.
- XOR Gate: Outputs high if only one input is high, low otherwise.
Truth tables clearly define each gate's behavior under all input scenarios. Referencing these can help decode what simple digital circuits constructed from logic building blocks will actually do.
Logic gate | Schematic symbol | Truth table |
AND | ||
OR | ||
NAND | ||
NOR | ||
XOR |
- AND gate: TI SN74HCS09
- OR gate: TI SN74HCS4075
- NAND gate: TI SN74HCS03
- NOR gate: TI SN74HCS27
- XOR gate: TI SN74HCS86
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