nRF52840 PWM second output pin not working properly

[Philip]

Hi. I am trying to output a square wave on to separate output pins. I want to have one inverted, however I can't even get the same output on both pins at the moment. The pin assigned to the second output on the PWM doesn't toggle like the first output, it just stays on whilst the PWM is enabled (see trace below).

Should the below PWM setup not result in both pins outputting the same signal?

When I swap them in software (so PWM_2 first) then they swap on the oscilloscope, so the 2 output pins are working.

void pwm_init(uint16_t freq)
{
    nrf_drv_pwm_config_t const config0 =
    {
        .output_pins =
        {
            COIL_PWM_1, // channel 0
            COIL_PWM_2, //channel 1
            NRF_DRV_PWM_PIN_NOT_USED,             // channel 2
            NRF_DRV_PWM_PIN_NOT_USED,             // channel 3
        },
        .irq_priority = APP_IRQ_PRIORITY_LOWEST,
        .base_clock   = NRF_PWM_CLK_16MHz,
        .count_mode   = NRF_PWM_MODE_UP,
        .top_value    = freq,
        .load_mode    = NRF_PWM_LOAD_INDIVIDUAL,
        .step_mode    = NRF_PWM_STEP_AUTO
    };
    // Init PWM without error handler
    APP_ERROR_CHECK(nrf_drv_pwm_init(&m_pwm0, &config0, NULL));
}

 

Thanks

[Philip]

Ok, I had to add the second channel into this function; 

"seq_values->channel_1 = duty_cycle;"

void pwm_update_duty_cycle(uint16_t duty_cycle)
{
    seq_values->channel_0 = duty_cycle;
    seq_values->channel_1 = duty_cycle;
    
    nrf_drv_pwm_simple_playback(&m_pwm0, &seq, 1, NRF_DRV_PWM_FLAG_LOOP);
}

[Philip]

Also if you add " | 0x8000 " at this point, then you can invert the output of a pin.

void pwm_update_duty_cycle(uint16_t duty_cycle)
{
    seq_values->channel_0 = duty_cycle;
    seq_values->channel_1 = duty_cycle | 0x8000;
    
    nrf_drv_pwm_simple_playback(&m_pwm0, &seq, 1, NRF_DRV_PWM_FLAG_LOOP);
}

[Susheel Nuguru]

Yes, we need to set the sequence values for each channel. Seems like it works now as intended?

[Philip]

Yes all working fine now.