Digital Electronics
In the digital world everything reduces to two levels: 0 (low, ~0 V) and 1 (high, ~5 or 3.3 V). Logic gates are the tiny decision-makers that process these bits. NOT inverts its single input: 0→1, 1→0. AND outputs 1 only if both inputs are 1: 00→0, 01→0, 10→0, 11→1. OR outputs 1 if at least one input is 1: 00→0, 01→1, 10→1, 11→1.
NAND and NOR are the inverted-output versions of AND/OR. NAND: 00→1, 01→1, 10→1, 11→0 (i.e. 0 only when all inputs are 1). NOR: 00→1, 01→0, 10→0, 11→0 (1 only when all inputs are 0). XOR (exclusive-OR) outputs 1 when the inputs differ: 00→0, 01→1, 10→1, 11→0 — it acts like an "inequality detector" and is the heart of adder circuits.
NAND and NOR are universal gates: on their own they can build every other gate, which is why they are the fundamental building block of IC manufacturing. Gate behavior is written with Boolean algebra: a dot for AND (A·B), a plus for OR (A+B), an overbar for NOT (Ā). In the next lesson we will see the simplification rules of this algebra.
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