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).
