[DFTMAX] Need help for scan compression

[maulin sheth]

Hello All,
I want to know that how DFTMAX working for Compression and Decompression?
I want to know that, What combo logic is used/inserted for Decompression and Compression?
Is there any specif reason to choose particular combo logic?
Pl help me to understand this.

Thanks & Regards,
Maulin Sheth

 

[assud]

Hi,

Compression/Decompression (codec) technique is used to effectively use the tester memory size and number of test inputs.
Codec logic uses internal scan chains with limited number of scan inputs.
In DFTMAX, 'mux' is used in decompression and 'xor' for compression. This is by considering the better controllability through mux and observability through xor logic.

DFTMAX userguide provides sufficient info.

 

[maulin sheth]

Thanks Aswathy.
I have done one small exercise in DFTMAX, but in that case, not any mux is used for the scan compression. But output side XOR is used...So I want to know that why this happens for decompression logic.
I have top level 3 scan-ins and after decompression logic, the 7 internal scan chain generated. But the logic is buffer and inverter. Not any Mux. Can you have any idea, why this happens.

 

[assud]

It happens due to the very low compression ratio.

 

[maulin sheth]

Thanks Aswathy.
I want to know another concept is that...In DFTMAX ,we can write SPF for basic scan and compressed scan. There is one common pin to switch between Basic and Compressed scan. I want to know that how it works on the same netlist? If I have the compressed scan inserted netlist than how stitching occurs to convert it into basic scan using single controlled pin?

 

[assud]

The pin used to select between the modes follows a decoder logic to control the select options for the scan stitching. The decoder outputs controls the activation of the internal mode or the compression mode chains.

 

[maulin sheth]

Thanks aswathy...
Again I also want to know that what is difference between X-masking and X-blocking. How to do it with DFTMAX? We have to do it manually or DFTMAX command is available?