how to specify internal net as scanmode signal

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animotion

Joined: 22 Aug 2009
Posts: 6
Location: Ireland

09 Oct 2009 22:12 how to specify internal net as scanmode signal

All,

I need to define a certain internal signal in my synthesized netlist to be the scanmode signal for DFT.

How is this possible in DFT compiler? (Do I use the set_sft_signal command..?)

In the netlist, this internal signal is the output of combinational logic. The input into
this logic is dft_tst<2:0>. i.e. the scanmode signal is one of the 8 dft_tst testmode settings.

-animotion

roli

Joined: 29 Apr 2001
Posts: 846
Helped: 1
Location: 'SiliconWafer' Island

10 Oct 2009 8:22 how to specify internal net as scanmode signal

Yes you can, only if the Tester (and DFTAdvisor) can fully access (via Primary Inputs) & control the combinatorial logic which outputs the internal 'scanmode' signal.

animotion

Joined: 22 Aug 2009
Posts: 6
Location: Ireland

10 Oct 2009 21:18 Re: how to specify internal net as scanmode signal

roli,

The tester will have access to (and control of) the dft_tst<2:0> which is the input to the combinatorial logic that controls the internal "scanmode" signal

Would you have the DFT Compiler command that ensures that the internal "scanmode" signal is recognised as such by DFT compiler?

Thanks
animotion

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michealwolf

Joined: 05 May 2008
Posts: 6

11 Oct 2009 4:08 Re: how to specify internal net as scanmode signal

you may try the option -hookup_pin of set_dft_signal.

roli

Joined: 29 Apr 2001
Posts: 846
Helped: 1
Location: 'SiliconWafer' Island

11 Oct 2009 11:50 Re: how to specify internal net as scanmode signal

animotion wrote:

Yes , assuming you define precisely (in DFTAdvisor) the exact combinatorial equation of "dft_tst<2:0>" which produces 'scanmode'.

animotion

Joined: 22 Aug 2009
Posts: 6
Location: Ireland

12 Oct 2009 16:44 Re: how to specify internal net as scanmode signal

roli,

I am using Synopsys DFT Compiler (in Design Compiler).
I am unaware of DFTAdvisor.

The command that I am using to get DFT compiler to recognize the internal scanmode signal is:

set_dft_signal -type TestMode -hookup_pin <hierarchical location of the gate that drives the scanmode signal> -active_state 1

This is not working and causes a scan chain violation which says that the chain is broken. The only problem is the internal scanmode signal.

Can you suggest how to improve this command or another command?

Regards,
Paul

Added after 1 minutes:

Roli,

The exact combinatorial equation of "dft_tst<2:0>" which produces 'scanmode' is 111.

-animotion

rsqf

Joined: 21 May 2007
Posts: 29
Helped: 2

13 Oct 2009 4:30 how to specify internal net as scanmode signal

I am sure that there is a command u can use. U mean the signal is generated by the other logic and control the whole chip to into scanmode?
I think u could set the signal to 111 (than the chip will be set in the scan mode). the command will be set_dft_signal -constant or test_hold something like that , u can search them using the keyword in the Synopsis DC reference doc.

pennsia

Joined: 27 May 2009
Posts: 12

13 Oct 2009 18:56 Re: how to specify internal net as scanmode signal

I used DFTAdvisor. The command is like:

1. add primary input /.../../scan_mode
which pulls out your internal signal and treats it as primary input

2. setup scan insertion -ten /.../../scan_mode -active high
which defines that signal to be your scan_mode

I believe DFT Compiler has the similar commands.