RE: Invert PWM Behaviour

Sigurd — Thu, 12 Apr 2018 10:56:38 GMT

If were using the PWM driver, the answer can be found here.

But, I see that you are not using the PWM driver, but accessing the PWM peripheral directly. In that case you need to set bit 15 in the buffer you provide in NRF_PWM0->SEQ[0].PTR to inverse the polarity.

Snippet:

int16_t buf[] = {(1 << 15) | 1500}; // Inverse polarity (bit 15), 1500us duty cycle
NRF_PWM0->SEQ[0].PTR = (uint32_t)&buf[0];

See the example here.

RE: Invert PWM Behaviour

Takeshi Goda — Thu, 12 Apr 2018 06:00:18 GMT

I am using this code to generate the PWM

NRF_PWM0->PSEL.OUT[0] = (first_pin << PWM_PSEL_OUT_PIN_Pos) |
(PWM_PSEL_OUT_CONNECT_Connected <<
PWM_PSEL_OUT_CONNECT_Pos);
NRF_PWM0->ENABLE = (PWM_ENABLE_ENABLE_Enabled << PWM_ENABLE_ENABLE_Pos);
NRF_PWM0->MODE = (PWM_MODE_UPDOWN_Up << PWM_MODE_UPDOWN_Pos);
NRF_PWM0->PRESCALER = (PWM_PRESCALER_PRESCALER_DIV_1 <<
PWM_PRESCALER_PRESCALER_Pos);
NRF_PWM0->COUNTERTOP = (16000 << PWM_COUNTERTOP_COUNTERTOP_Pos); //1 msec
NRF_PWM0->LOOP = (PWM_LOOP_CNT_Disabled << PWM_LOOP_CNT_Pos);
NRF_PWM0->DECODER = (PWM_DECODER_LOAD_Common << PWM_DECODER_LOAD_Pos) |
(PWM_DECODER_MODE_RefreshCount << PWM_DECODER_MODE_Pos);
NRF_PWM0->SEQ[0].PTR = ((uint32_t)(seq0_ram) << PWM_SEQ_PTR_PTR_Pos);
NRF_PWM0->SEQ[0].CNT = ((sizeof(seq0_ram) / sizeof(uint16_t)) <<
PWM_SEQ_CNT_CNT_Pos);
NRF_PWM0->SEQ[0].REFRESH = 0;
NRF_PWM0->SEQ[0].ENDDELAY = 0;
NRF_PWM0->TASKS_SEQSTART[0] = 1;

The first waveform it generates is low level and I need high level