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Design with Multiplexers :

  • The first method of realizing a logic circuit from the ASM chart simplify using the K-map simplification. We have discussed this method in the preceding section.
  • The other method of realization is by using the multiplexers. We will discuss this method in this section.
  • A combinational circuit can be implemented with the help of multiplexers instead of individual gates. Hence we are going to replace the combinational circuit that uses gates by a multiplexer.
  • The multiplexer method of design has three levels of components, as shown in Figure below.

  • The multiplexer outputs are applied to the flip flops forming the register at second level. The second level register is used for holding the present binary state.
  • The multiplexers decide the next state of the register because multiplexer output has been connected to the flip-flop inputs as shown in Figure.
  • The third level has a decoder which provides a separate output for each control state. Sometimes the decoder is replaced by a combinational circuit.
  • The input to this decoder come from the outputs of the register flip flops and the inputs X1, X2 etc.
  • In order to understand the design with multiplexers let us use the same waveform generator example.