Question on pwm using due

hi all,

i newbie in arduino due , when trying due generate pwm, found behavior cannot explain.

i called on pin 7, , default frequency 1 khz , uses signal pwm clock a, no problem.

then, went change register pwm clock register value , try higher. according due cpu datasheet, when set prea , diva value clock has same frequency mck, expecting close 84 mhz instead, got square wave of 329 khz (still 50% duty cycle), 84 mhz / 255.

i don't see anywhere else on pwm section of datasheet 1 can divide mck frequency. confused on 255 coming from. if can make use of divider, helpful.

here code:

code: [select]


#include <spi.h>
#define pwm_wpcr    (*(volatile unsigned long int *) 0x400940e4)  //datasheet 1053
#define pwm_clk    (*(volatile unsigned long int *) 0x40094000) // datasheet 1020
void setup() {
    analogwrite(7, 127);

   pwm_wpcr = 0x50574d3c; // disable write protection pwm
    pwm_clk = 0x00000001; // clk mck, disable clk b
}


i have looked channel mode register, if uses clk or clk b, there 1 option without divider. please find link datasheet here: http://www.atmel.com/images/doc11057.pdf

thanks time. appreciated.

f33d

for pwm, actual clock rate pwm frequency times pwm count. 8 bit resolution, count 255.

therefore max pwm frequency 8 bit resolution mck/255, have found.

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