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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)


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