In ad9249 datasheet, The PN sequence short pattern produces a pseudorandom bit sequence that repeats itself every 511 bits(ITU 0.150 X^9+X^5+1).The seed value is all 1s. The output is a parallel representation of the serial PN9 sequence in MSB-first format.The first output word is the first 14 bits of the PN9 sequence in MSB aligned form.

Sequence Initial value Next three output samples (MSB first) twos complement

PN sequence short 0X1FE0 0X1DF1 , 0X3CC8, 0X294E

I don't undersand that why the initial value is 0X1FE0 since that the seed value is all 1s. And if I take the first 9 bits of the initial value into X^9+X^5+1 , the calculation results don't agree with the next three output samples.

I want to konw why the initial value is 0X1FE0 and how to calcaulate the next output. thanks!

Dear 肖大屌,

Thanks for your interest in AD9249. I'm sorry about the confusion.

The seed value is all 1s. 0x1FE0 is the

nextvalue after the shift register has been advanced 14 bits (because AD9249 is a 14 bit converter). The use of the word "initial" is misleading; I apologize.The next thing to realize is that, the values listed in the datasheet are in 2s Complement format. In your calculator or simulator, you are likely working with 1s and 0s. You will need to convert the binary result to 2s complement by inverting the MSB (Bit13).

So, in summary:

Please let me know how it goes.

Thanks again.

Doug