Multiplexer
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Multiplexing is selecting one of many analog or digital input signals and outputs that into a single line. A multiplexer of 2n inputs has n select bits, which are used to select which input line to send to the output. An electronic multiplexer makes it possible for several signals to share one device or resource, for example one A/D converter or one communication line, instead of having one device per input signal. A demultiplexer is a device taking a single input signal and selecting one of many data-output-lines, which is connected to the single input. A multiplexer is often used with a complementary demultiplexer on the receiving end.
Chart 74HC138N
This chart shows demux (74HC138N) operation, 3-to-8 line decoding. On this device all outputs are inverted, meaning negative when active. This is indicated by the tailing N in 74HC138N. Different combination's of the inputs; A1, A2 and A3 will trigger different outputs (Yx).
Images
 Circuit with LED-display and demultiplexer |
 Multiplexer |
