Multiplexers/Demultiplexers

Objectives

1. Examine multiplexers

Notes

• Continuing in Carpanelli chapter 4
• A multiplexer or mux allows us to select one imput among 2ⁿ inputs.
  • There are 2ⁿ input lines (d₀ through d^k)
  • There is 1 output line
  • There are n control lines, k = 2ⁿ
• For example
  • 
  • There are 4 inputs (d0 - d3)
  • There are 2 control bits
  • There is 1 output
• The mux will select one of the data inputs and transfer it to the output based on the control bits.
• This is really just a decoder with a data transfer function.
  • 
• The author points out that some muxes have an enable line
• So they can be chained like we did with decoders.
• The 74x151 is a 8 input mux
  • Data in and out, control as expected
  • Data out is calle Y
  • Plus a not line for the data out (W)
  • The enable line is a enable not (S on the digital implmeentation, but G on the datasheet.
  • See the datasheet.
  • 
• A demultiplexer is the opposite
  • 1 input line
  • 2ⁿ output lines
  • n control lines
  • 
• Implementation uses a decoder
  • 
• The 74238 is a decoder and a mux
  • We have probably looked at it as a decoder.
  • We will use The G line as data in. And GA and GB are enable not lines.
  • 
• The digital file