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ID: 1534
Case Type: faq
Category: Implementation
Related To: IPexpress
Family: All FPGA

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When implementing the Linear Feedback Shift Register (LFSR) Arithmetic Module in IPexpress, How do I set the "Feedback Polynomial"?

This question can be answered best by going over an example.


Let's assume you would like to  implement a 64-bit LFSR with polynomial X^64+X^4+X^3+X^1+1 .


Excluding the + 1 at the end of the polynomial above, you should create a binary string that represents each coefficient (1 or 0 depending on whether it is present in the equation) for each of X^1 through X^64:

X^64..............................................................X^1
   1000000000000000000000000000000000000000000000000000000000001101

Then , convert this binary string to hexadecimal: 800000000000000D

You should now enter this hexadecimal value into the Feedback Polynomial field.