What does scan chain do in a design?

[chanducs24]

Hi

can anyone decsribe about scan chain like what it does in design? why they have been using?

chandra.

 

[yadavvlsi]

Re: Regarding scan chain

Scan chains are added to make the design testable..! If there is a fault ( like STUCK at 0 or STUCK at 1) in the circuit, it can be detected if it is OBSERVABLE at primary output by CONTROLLING the primary inputs of circuit. Fault is propagated to primary output using scan chains.!

 

[jeevan.life]

Re: Regarding scan chain

Scan chains are added to make the design testable..! If there is a fault ( like STUCK at 0 or STUCK at 1) in the circuit, it can be detected if it is OBSERVABLE at primary output by CONTROLLING the primary inputs of circuit. Fault is propagated to primary output using scan chains.!

Exactly...the method to do it is to insert a mux in the design so that the chip can be made to run in scan mode or functional mode...

 

[lohi21]

As they said above,

It is used for the DFT (Design for test) to test the controllability and observability.

In DFT insertion, All FFS are converted with the muxed FF. so while at DFT mode, normal functionality of the design is disabled and vice versa.

Scan chain means, The FF's are connected in FIFO way and will be used to check for controllability and observability in scan mode.