FTM PWM input filter

Lauch_Spargel — Mon, 15 Nov 2021 11:08:45 GMT

Hello,

is there a example for a FTMinput filter configuration?

I would like to debounce a pwm signal. Is the FTM filter useful for this application or should I implement the debouncing with software? Or is there a fitler by default? And are there pullup or pulldown resistors at the input pins?

This is the FTM configuration I am using.

/* - Dual-Edge Capture Mode */ void FTM0_Dual_Edge_Capture_Mode() { /* Enable clock for PORTD */ PCC->PCCn[PCC_PORTD_INDEX] = PCC_PCCn_CGC_MASK; /* Select and enable clock for FTM0 */ PCC->PCCn[PCC_FTM0_INDEX] = PCC_PCCn_PCS(6) | PCC_PCCn_CGC_MASK; PORTD->PCR[15] = PORT_PCR_MUX(2); // Set PTD15 for FTM0 - Channel0 S32_NVIC->ISER[FTM0_Ch0_Ch1_IRQn / 32] |= (1 << (FTM0_Ch0_Ch1_IRQn % 32)); // Enable interrupt /* Enable dual-edge capture mode */ FTM0->COMBINE= FTM_COMBINE_DECAPEN0_MASK | FTM_COMBINE_DECAP0_MASK | FTM_COMBINE_DECAPEN1_MASK | FTM_COMBINE_DECAP1_MASK; /* Set CNTIN */ FTM0->CNTIN = FTM_CNTIN_INIT(0); /* Select positive polarity pulse width measurement and enable continuous mode for FTM0_CH0 */ FTM0->CONTROLS[0].CnSC = FTM_CnSC_MSA_MASK | FTM_CnSC_ELSA_MASK; FTM0->CONTROLS[1].CnSC = FTM_CnSC_ELSB_MASK | FTM_CnSC_CHIE_MASK; /* Reset counter */ FTM0->CNT = 0; /* Select clock */ FTM0->SC = FTM_SC_CLKS(1) |FTM_SC_PS(7); FTM0->MOD = 62500 -1 ; /* FTM1 counter final value (used for PWM mode) */ /* FTM1 Period = MOD-CNTIN+0x0001 ~= 62500 ctr clks */ /* 8MHz /128 = 62.5kHz -> ticks -> 1Hz */ }

Re: FTM PWM input filter

PetrS — Tue, 16 Nov 2021 09:35:22 GMT

Hi,

yes, the FTM input filter can be used , see more in chapter 47.5.5.1 Filter for Input Capture Mode of teh RM. It is enough to set FILTER[CH0FVAL] and SC[FLTPS] values.
For example https://community.nxp.com/t5/S32K/About-the-S32K146-FTM-input-capture-filter-function/m-p/1245500 discusses filtering time calculation

BR, Petr

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