Selecting circuits - decoders
  a. Decoder - converts an address into a one of n unique choices.
    i. N address lines, 2^n select output lines.
   ii. Select banks of memory 
       or specific task circuit in CPU (instruction decoder). 




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Routing circuits 
  a. Demultiplexer - routes single input to one of several alternative outputs.
    i. Uses set of address lines to select desired output line.
   ii. One input, 2^n outputs, n select(address) lines.
   * Serial to parallel data conversion.  External device selection.




  b. Multiplexer - routes one of several inputs into a single output.
    i. Uses set of address lines to select desired input line.
   ii. 2^n inputs, one output, n select(address) lines.
   * Useful when transmitting data on serial lines (SATA, USB, Ethernet).
  iii. Used as row/address selector in DRAM memory.



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