multiple scan chain in testing

[jincyjohnson]

if there are multiple scan chain, and if each scan chain is of length L, the primary input is of length m.from multiple L bit scan chain,how can we give m primary inputs

 

[maulin sheth]

Hello,
Can you please tell what you want exactly?
What do you means by Primary input is of length m?
Do you want to say that m is the number of primary inputs?

So can you please clarify your question more clearly?

Maulin

 

[jincyjohnson]

Suppose there are four scan chains whose lengths are 8 ina full-scan design. The 8-bit Johnson codewords and 4-bit (or more bits) seeds can be used to generate an MSIC sequence. A MSIC sequence with seed 01101 is
chain 1 chain 2 chain 3 chain 4 primary inputs

X(1) 10000000 ` 10111111 11011111 00010000 01101
X(2) 11000000 10011111 11001111 00011000 01101
X(3) 11100000 10001111 11000111 00011100 01101
-------------------------------
------------------------
X(16) 00000000 11111111 11111111 00000000 01101

How can we set the number of bits in seed.It depends on which parameter.Is there any criteria of choosing number of seed bits as four.In this example, i think the number of bits in primary input is 5.Or is it 4?.In this multiple scan chain how can we give the primary inputs.In which order we can give the primary inputs.Because each chain length is 8 bit and there are 4 chains. whether the ISCAS 85 and ISCAS 89 bench mark circuits are inbuilt with any fault or we have to manually insert fault.How can we know that how much test vectors are required to detect fault. Can you also explain the procedure of inserting fault and how it is detected.Thanks in advance.

 

[maulin sheth]

Hello,
I think you are very confused.
I think you first need to clear about the testing using scan chain....scan chain is a chain of flip flops without any combo logic in between two consecutive flops.
We just load the flip flops using the scan chain...
and primary inputs are separate from scan chain inputs...so first load the flops thn apply the primary inputs.....
How many patterns are required to detect any fault? The answer is that it is not fixed....its totally depends on the testability of test node.
For inserting the fault you just appy pattern and thn you just need to force some internal instance input to opposite value...so you can get that the pattern is working fine or not...

You first need to clear the scan testing basics.....so you can get the better idea....