1 Digital Logic DesignWeek 7Encoders, Decoders, Multiplexers, Demuxes
2 MSI (Medium Scale Integration) Circuits (chips) MSI chips have complete circuits, built from multiple gates, on a single chip.Two classes of such integrated chips (ICs) are:Encoders and DecodersMultiplexers and DemultiplexersAre designed and based on binary coded input.
4 10 key numeric keypad data encoded into 4-bit binary code. EncodersEncoders typically have 2N inputs and N outputs.These are called 2N–to–N encoders.Typical examples include 4–to–2 encoders (probably not used much)8–to–3 encoders16–to–4 encodersIt is assumed that only one input at a time is active.10 key numeric keypad data encoded into 4-bit binary code.Due to the decimal arithmetic, we also have 10–to–4 encoders. (Why not 10:3?)
5 ExerciseWrite the truth table for the 10:4 decimal keypad encoder and boolean expressions of each output. Draw the circuit diagram.The Circuit Diagramfor the 10–4 EncoderInput (10 bits) codeOutput codeD9 through D0Y3Y2Y1Y01In the above encoder, one should note that the input D0 is not connected to any output. An output of 0000 always implies that button 0 is pushed.Y3 = D8 + D9, Y2=… , Y1=… , Y0=…
6 DecodersDecoders are the opposite of encoders; they are N–to–2N devices.Typical examples include 2–to–4 decoders3–to–8 decoders4–to–16 decodersoptionally, they may have an enable lineactive-high or active-low (the selected output goes to logic 0)used for to convert n bit binary information to 2n unique outputs
13 MultiplexerRS D-Type Serial Port Data Multiplexer
14 A 2-input multiplexerQuadruple 2-Line To 1-Line Data Selectors/MultiplexersDefinition: An n-input multiplexer (called a MUX) is an n-way digital switch that switches/directs/routes one of ‘n’ inputs to the output line.controlled by the control lines ‘S’ to select which input line to be “connected” to the output.means that the logical value of the output will be the same as the logical value of the selected input.