5.4 Decoders- A decoder is a multiple-input, multiple-outputlogic circuit that converts coded inputs intocoded outputs, where the input and outputcodes are different. The input code generally hasfewer bits than the output code, and there isone-to-one mapping from input code words intooutput code words.inputmapcode wordoutputcode wordenableinputsDecoder
5.4 Decoders Return Next ◼ A decoder is a multiple-input, multiple-output logic circuit that converts coded inputs into coded outputs, where the input and output codes are different. The input code generally has fewer bits than the output code, and there is one-to-one mapping from input code words into output code words. input code word output enable code word inputs Decoder
5.4 DecodersBinarydecoder The most common decoder circuit is an n-to-2ndecoder or binary decoder. Such a decoder hasan n-bit binary input code and a 1-out-of-2noutput code.Truthtablefora2-to-4binarydecoder2-to-4InputsOutputsDecoder10EN11Y3Y2Y1YO10YO0000110XXY10000011Y2n00ENY311"don't-care"001001notation
5.4 Decoders ◼ Binary decoder ➢ The most common decoder circuit is an n-to-2 n decoder or binary decoder. Such a decoder has an n-bit binary input code and a 1-out-of-2 n output code. Truth table for a 2-to-4 binary decoder Inputs Outputs EN I1 I0 Y3 Y2 Y1 Y0 0 X X 1 0 0 1 0 1 1 1 0 1 1 1 0 0 0 0 0 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0 2-to-4 Decoder I0 Y0 I1 Y1 Y2 EN Y3 Return Back Next ”don’t-care” notation
5.4 DecodersY1= 11:10.ENY0=11.10.ENY3 = 11. 10. ENY2=J1:J0.EN10YO12Y3ENSimulation
5.4 Decoders Return Back Next Y0 = I1I0EN Y1= I1I0EN Y2 = I1I0EN Y3= I1I0EN Simulation
5.4 Decoders It is not necessary to use all of the outputs of adecoder, or even to decode all possible inputcombinations, e.g. a decimal or BCD decoderLogic Symbols for Lager-Scale Elements> The most basic rule is that logic symbols aredrawn with inputs on the left and outputs on theright. The top and bottom edges of a logicsymbol are not normally used for signalconnections. However, explicit power and groundconnections are sometimes shown at the top andbottom, especially if these connections are madeon “nonstandard" pins.RetumBack
◼ Logic Symbols for Lager-Scale Elements ➢ The most basic rule is that logic symbols are drawn with inputs on the left and outputs on the right. The top and bottom edges of a logic symbol are not normally used for signal connections. However, explicit power and ground connections are sometimes shown at the top and bottom, especially if these connections are made on “nonstandard” pins. 5.4 Decoders ➢ It is not necessary to use all of the outputs of a decoder, or even to decode all possible input combinations, e.g. a decimal or BCD decoder. Return Back Next
5.4 Decoders We use an inversion bubble to indicate anactive-low pin and the absence of a bubble toindicate an active-high pin.> Active-high pins are given the same name as theinternal signal, while active-low pins have theinternal signal name with an overbar.external1/2 74X139pinGGYOYoy1Y1internalAAY2Y2signalBY3BY3RtumBak
5.4 Decoders ➢ We use an inversion bubble to indicate an active-low pin and the absence of a bubble to indicate an active-high pin. Return Back Next 1/2 74X139 G Y0 Y1 A Y2 B Y3 G A B Y0 Y1 Y 2 Y3 ➢ Active-high pins are given the same name as the internal signal, while active-low pins have the internal signal name with an overbar. internal signal external pin