Scan chain

Scan chain is a technique used in design for testing. The objective is to make testing easier by providing a simple way to set and observe every flip-flop in an IC.The basic structure of scan include the following set of signals in order to control and observe the scan mechanism.Scan_in and scan_out define the input and output of a scan chain. In a full scan mode usually each input drives only one chain and scan out observe one as well. A scan enable pin is a special signal that is added to a design. When this signal is asserted, every flip-flop in the design is connected into a long shift register. Clock signal which is used for controlling all the FFs in the chain during shift phase and the capture phase. An arbitrary pattern can be entered into the chain of flip-flops, and the state of every flip-flop can be read out.

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