[Problem] insert scan isnt working -Please help

[Karthikeya]

Hi everyone,
I am trying to insert a scan chain to a digital block containing serial interface, registers and io programmable, etc. The package pin is scan enable signal whereas the scan in scan out and scan clk are all generated within (by muxing the serial inputs). When I do the compile -scan it replaces all the DFFs with scan FFs but when I do insert_scan I see only some of the blocks to be replaced with scan FFs while the rest is still DFFs and a scan chain is formed with them.
I dont know much about the dft techniques. So please help me.

Regds
Karthik

 

[dft_guy]

It's probably an internal shift register that is already hooked up serially. I believe the newer versions of DFTC automatically detect shift registers, and perform scan replacement on only the first FF in the register. This helps save area - if you have an internal shift register, it can be used untouched as part of the scan chain.

John
DFT Digest