An expression is a compact description of a logic rule; a truth table lists its answer for every input combination. For n binary inputs, there are 2^n rows. Evaluate the expression one operation at a time, keeping intermediate columns when the rule becomes complicated.
Worked example
For F = A AND NOT B, list AB as 00, 01, 10 and 11. NOT B is 1, 0, 1 and 0. Combining that column with A gives F = 0, 0, 1 and 0. Thus only the row A = 1, B = 0 turns the output on.
What to watch for
Use parentheses rather than relying on an unclear operation order. A missing row can hide an incorrect implementation.
Try it yourself
How many rows does a complete four-input truth table require?
Answer: 2^4 = 16 rows. Every possible input pattern needs one output entry.
How to study this topic
Read one operation at a time and use parentheses generously. Check a simplification with every truth-table row, not just a convenient example. A useful simpler expression must preserve the complete specified function.
Explore related programmes
These recorded programmes are upcoming. This article is general educational content, not a syllabus or course sample.
Digital Electronics