scan register

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scan register - Free On-line Dictionary of Computing (26 May 2007) :

  scan register
  
     (circuit design) A digital logic circuit which can act
     either as a flip-flop or as a serial shift register and
     which is used to form a scan path.
  
     The most common design is a multiplexed flip-flop:
  
     	      ___	  ____
      normal in --|	 \	 |    |
     	     |	  |------|D  Q|---- normal/scan output
      scan in ----|___/ mux	 |    |
     	       |	 |    |
      test mode ----+    +----|>   | flip-flop
     		    |	 |____|
      clk ---------------+
  
     The addition of a multiplexor (mux) to each flip-flop's
     input allows operation in either normal or test mode.  The
     output of each flip-flop goes to the normal functional logic
     as well as to the scan input of the next multiplexor in the
     scan path.
  
     The other common design is level-sensitive scan design
     (LSSD).
  
     (1995-02-14)