Basic question about EDT

[honey13]

I have one basic question regarding edt, mentor compression tool.

As shown in the figure the entire chain is between scan_in and scan_out pins.This is the case with EDT on.Then where is the case of decompressor and Compactor.

When edt is off, in that case i am seeing the decompressor and compactor related cells in the scan chain.

Can someone explains me why is this.

 

[jducluzeau]

Re: Basic EDT Question

EDT decompressor is between scan inputs and first flop to scan.

My understanding is you didn't exclude flop of EDT when you inserted yours scan chain. Exactly the same way you excludes FF from JTAG.

Regards,
Jerome

 

[honey13]

Re: Basic EDT Question

hi Jerome,
Can you please elaborate this.What is this excluding flop of EDT.

 

[jducluzeau]

Re: Basic EDT Question

I guess scan chains are inserted during synthesys. I dont know what tool you used. but you need to define edt blocks as no scan blocks

 

[sajjaudaykumar]

Re: Basic EDT Question

Expanding on jducluzeau , Mentor recommends to add EDT in the no-faults list, so I guess u don't need to scan them.

 

[honey13]

I saw all the edt logic as combo, hence not coming in the scan chains. Please correct me if i am wrong.

Could any one share more info on EDT.

 

[jducluzeau]

I m little bit confused.
In your first messages, you wrote "When edt is off, in that case i am seeing the decompressor and compactor related cells in the scan chain."
and now EDT is a combo

 

[honey13]

Hi jducluzeau,
I was mistaken.There wont be any decompressor and compactor logic in fastscan.In fastscan i.e.., in edt bypass we wont have any concept of decompressor and compactor as the compression is disabled.

Do any one have idea about edt in bypass mode.
In edt bypass mode when edt_bypass signal is made 1 it concatinates the scan chains,the input of the first mux comes from a scan channel i/p while the output of last mux goes to scan channel o/p. this is my understanding of edt bypass.Please correct me if i am wrong.

In the case of edt bypass on the tool will uses the same number of scan channels as fast scan.In the bypass mode does compression takes place or not?

 

[sajjaudaykumar]

In the case of edt bypass on the tool will uses the same number of scan channels as fast scan.In the bypass mode does compression takes place or not?[/QUOTE]
a) yes the channels are always the same. Thats the point of using EDT. To the tester it looks like say 8 scan channels, but internaly when conpressed it the more that 8 chains..
b) In bypass there is no compression.

 

[honey13]

Hi sajjauday,
Is that edt bypass on means switching off the edt. If it is so what is the difference between the fastscan and edt in bypass mode.

 

[sajjaudaykumar]

Is that edt bypass on means switching off the edt.
A) yes.
If it is so what is the difference between the fastscan and edt in bypass mode.
A) Fastscan can't run if bypass is not on(edt ON). You can use EDT only with testKompress. In testKompress u can use only EDT(not sure!! Have never tried).

 

[honey13]

Hi sajjauday,

I understood it.Thnx.

Testkompress can be used to run in both modes edt and edtbypass.On turning off edt it behaves as fastscan.

 

[jakejake]

bypass will help you do diagnosis.

 

[sajjaudaykumar]

Hi All,
Does mentor have a tool to help diagnose failures in EDT mode(exact failing bit). Right now we run BYPASS mode which takes a long time to find the exact failure bit.