How to change the GPIO output frequency of nRF52832 over 1MHz ?

[Wesley_Lai]

Dear Sir,

I had a project is lighting the LED matrix, we choose the LED IC is TLC5958 and MCU is using nRF52832.

Now, we have a question is how to change the GPIO output frequency ?

After calculation, the LED IC clock needs 1.524MHz, but we try to pass the C language or modify the assembly language, GPIO can only output 1MHz.

Have any friends can help us ?

Thank you.

Wesley

2018.07.23

[Turbo J]

You can generate 1.6 MHz using a PWM peripherial. You might need to put the GPIO pin in high drive mode in order to achieve a good signal.

[Sigurd]

Hi Wesley,

Here is a bare-metal code example to get the PWM peripheral to output 1.6MHz on pin 4:

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#include <stdbool.h>
#include <stdint.h>
#include "nrf.h"
#include "app_error.h"
#include "nrf_delay.h"

#define PWM_PIN 4

int16_t buf[] = {(1 << 15) | 5}; // Inverse polarity (bit 15)


int main(void)
{

    // Start accurate HFCLK (XOSC)
    NRF_CLOCK->TASKS_HFCLKSTART = 1;
    while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) ;
    NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;

    // Configure PWM_PIN as output, and set it to 0
    NRF_GPIO->DIRSET = (1 << PWM_PIN);
    NRF_GPIO->OUTCLR = (1 << PWM_PIN);


    NRF_PWM0->PRESCALER   = PWM_PRESCALER_PRESCALER_DIV_1; // 
    NRF_PWM0->PSEL.OUT[0] = PWM_PIN;
    NRF_PWM0->MODE        = (PWM_MODE_UPDOWN_Up << PWM_MODE_UPDOWN_Pos);
    NRF_PWM0->DECODER     = (PWM_DECODER_LOAD_Common       << PWM_DECODER_LOAD_Pos) | 
                            (PWM_DECODER_MODE_RefreshCount << PWM_DECODER_MODE_Pos);
    NRF_PWM0->LOOP        = (PWM_LOOP_CNT_Disabled << PWM_LOOP_CNT_Pos);

    NRF_PWM0->COUNTERTOP = 10; 


    NRF_PWM0->SEQ[0].CNT = ((sizeof(buf) / sizeof(uint16_t)) << PWM_SEQ_CNT_CNT_Pos);
    NRF_PWM0->SEQ[0].ENDDELAY = 0;
    NRF_PWM0->SEQ[0].PTR = (uint32_t)&buf[0];
    NRF_PWM0->SEQ[0].REFRESH = 0;
    NRF_PWM0->SHORTS = 0;

    NRF_PWM0->ENABLE = 1;
    NRF_PWM0->TASKS_SEQSTART[0] = 1;


    while (true)
    {
    __WFE();

    }

}


/** @} */