Posts: 2
Registered: ‎04-17-2017

AN142 FFT Routines for the C8051

I have been attempting to use the FFT Routines as found in AN142 (Rev 1.1 12/03). So far my results do not appear correct, and do not agree with other FFT calculators.


A search of this forum suggests there were corrections make to AN142 after Rev1.1.

Is there a more recent (corrected) version available?


Posts: 1,728
Registered: ‎10-14-2014

Re: AN142 FFT Routines for the C8051

i checked but did not find a newer version than 1.1.
do you mind elaborating your issue more in detail and tell me what error you are having now.
if you could give me the link to the post that mentioned the correction it would also help.
Posts: 2
Registered: ‎04-17-2017

Re: AN142 FFT Routines for the C8051

Hello Delu, thanks for your reply.

I thought it best to verify that I had the most recent version of the application with any corrections before getting too much into details.

The actual processor used is a C8051F020.

I am using IntFFT_BRIN.C. I have set the sample size to 8 and 'No window' (WINDOW_TYPE = 0)

Input data is assumed to be differential, (SE_data = 0).


Inputting 8 sample points from one period of a 60 Hz sine wave into real array to test. I am expecting to see a single spike in the output representing the 60 Hz signal, but so far does not look correct.


I have very  limited internal Ram available to use so I did change the variable allocation to use xdata. Not sure if this may be the problem. I may try freeing up some internal RAM and trying again without this modification.


The link to the post that I mentioned is:


There are some suggested corrections in the thread.


Final post in the thread is from Silicon Labs employee advising that an updated revision with corrections will be made available (2007):


Re: an142 - adapting fft example code for using complex inputs


Thank you for pointing out these errors with AN142. I've entered the issues into our database and the next revision of AN142 will contain these changes.

If you have any other problems or questions, you can contact us directly using or

Best Regards,
Tabitha Parker
MCU Applications and Support Manager
Silicon Laboratories