Digital Electronics and Logic Basics
What this domain tests
Digital Electronics and Logic Basics tests binary numbers, logic gates, truth tables, Boolean simplification and simple combinational blocks. Expect questions that require reading a gate diagram or completing a truth table.
Core rules
- Binary place values are 8-4-2-1 for four bits. Convert by adding weights where the bit is 1.
- AND gives 1 only when all inputs are 1; OR gives 1 when any input is 1; NOT inverts; XOR gives 1 when inputs differ.
- NAND and NOR are universal gates: any logic function can be built from either alone.
- De Morgan: (A·B)' = A' + B' and (A + B)' = A'·B'.
- Active-low signals are marked with a bar or suffix; a logic 0 asserts them. Combinational output depends only on present inputs; sequential circuits use flip-flops and clock.
Worked example
Simplify Y = A·B + A·B'. Factor A: Y = A(B + B'). Since B + B' = 1, Y = A·1 = A. Check with a truth table: when A = 0, both product terms are 0; when A = 1, B = 0 makes A·B' = 1 and B = 1 makes A·B = 1. The output always equals A, so the two-input circuit can be replaced by a direct connection to A.
Traps
Treating XOR as OR: 1 OR 1 = 1, but 1 XOR 1 = 0. Forgetting that NAND is AND followed by inversion. Misreading active-low labels. Building a circuit before simplifying, which uses more gates and creates more wiring faults. Also check binary conversion from right to left, not left to right.