Combinational Logic ICs
A combinational logic circuit's output depends only on its present inputs. It has no intentional memory of previous states.
Decoders
A decoder converts a binary input into one of several selected outputs. A 3-to-8 decoder, for example, can activate one of eight outputs from a three-bit code.
Applications include memory selection, address decoding, display selection, and one-of-many control signals.
Encoders
An encoder performs the reverse idea: one of several inputs is converted into a binary code. Priority encoders also decide which input wins if several are active at once.
Multiplexers
A multiplexer, or MUX, is an electronic selector switch. Control inputs choose which one of several data inputs reaches the output.
Demultiplexers
A demultiplexer directs one data input toward one of several outputs. Some decoder ICs can also perform demultiplexing.
Comparators
A digital magnitude comparator indicates whether one binary number is less than, equal to, or greater than another.
Adders
A half-adder adds two one-bit numbers. A full-adder also accepts a carry input. Multiple full-adders can be cascaded into a binary adder.
Arithmetic logic units
An ALU combines arithmetic and logic operations. The classic 74181 is a historically important 4-bit ALU that could be cascaded to form wider processors.
Parity generators and checkers
XOR networks can add or verify a parity bit so simple transmission errors can be detected.
BCD-to-display decoders
ICs such as the CD4511 convert a four-bit binary-coded-decimal input into seven segment-control outputs for numeric displays.
Propagation through combinational logic
A combinational network does not switch everywhere simultaneously. Different logic paths can have different delays, briefly creating glitches or hazards. This becomes important when outputs directly control clocks, asynchronous resets, or other timing-sensitive inputs.