56F800DEMO problem with FIR Filter

Started by November 30, 2006
Hi, I'm Mateo

We are Trying to implement a FIR Filter with a 56F800DEMO Board, outputing the signal via PWM, in audio band.

The timer C2 is set for 8Khz, so the ADC is sampling with that clock base.
The PWM is set for reload every cycle and its Frequency is also 8KHz.
No matter the taps setting, we always have at the PWM output, some sort of impulse response "drived" by the input signal. The output is always "overdrived".The output is not noisy, is a perfect impulse response with ripple as claerly defined lobules.

We haven't set the PWM for a syncronous output, but when we tried to output the input signal without processing we didn't have any problem (except for the harmonic content in base band, proper of PWM modulation).

We're using the DSP_Func_DFR Bean for implement the filter.

The variables (We change from the unsigned short generated by the ADC in a Frac16 Type accepted in the FirCreate structure).

Where is the problem?, the PWM syncro?. It is posible to realize what we are trying to do?.

Please if Know something about it, please let me know. Many things in my life (and my mate's life)depends on it. If I don't get my graduation in december my life will be awful.


Mateo Carabajal. Viva Peron.