How to understand seed and generator's polynomial in modulation toolkit

Question

I'm new in modulation toolkit. I wonder, e.g., for MT Generate
BitStream.vi, why I did not see the format for PN sequence generator's
polynomial? Is it default to something?
On the other hand, seed means the initial state of PN generator shift
register. why does it default to 0xD6BF7DF2? Can I set to 0 or 1?
Thanks.

Answer 1

Hello keiylh,
I am assuming that you are referring to MT Generate Bits.vi. You can use any number than zero to specify seed. If you give zero as seed, the generator will be continuously generating zeros (This is referred to as degenration).
If you open the block diagram for MT Generate Bits.vi, you will find "mod_Generate Bits PN Sequence.vi". This VI is creating the pseudo random bit sequence.
The subVI "mod_GF2 Primative Poly LUT.vi" stores the polynomial co-efficients of a PN sequence in an array.
Let me explain:
1) If you specify PN sequence as 9, from mod_GF2 Primative Poly LUT.vi's array, we will get the 9th index which is 10001. This is XORed with the sequence in the while loop
2) 10001 corresponds to polynomial, 1* X0 (corresponds to LSB)+0* X1+0* X2+0* X3+1* X4 (where XN --- X power of N)  which is X0+X4.This is implemented  in LabVIEW using XOR's.
Please let me know if this helps.
Kalyan
Kalyanramu Vemishetty
Automated Test Systems Engineer
National Instruments