Floating outputs when not connected to PWM Timer 8

[Tobe]

Hi, 

i found out, that the output is floating, when it is not activated to output the PWM signal of timer 8.

// **************** PWM *********************
	// PC6-8 (High side)
	// PC10-12 (Low side)
	my_GPIO_InitStruct.Pin = 	GPIO_PIN_6 |
								GPIO_PIN_7 |
								GPIO_PIN_8 |
								GPIO_PIN_9 |	// TODO: debug pin mod: PC9: remove test for tim 8 CCR4 (see other, and change back to EEPROM)
								GPIO_PIN_10 |
								GPIO_PIN_11 |
								GPIO_PIN_12;

	my_GPIO_InitStruct.Mode = GPIO_MODE_AF_PP;
	my_GPIO_InitStruct.Pull = GPIO_PULLDOWN;	// Pulldown, to never create an opportunity of shootthrough. Actually not used by timer, directly, but may be used by software (intentionally or accidently).
	my_GPIO_InitStruct.Speed = GPIO_SPEED_LOW; // Low = 270V/us / fast = 570V/us
	HAL_GPIO_Init(GPIOC, &my_GPIO_InitStruct);

	// Alternative function HIGH register
	GPIOC->AFR[0] |= (	GPIO_AFRL_AFSEL6_2 |  	// AF4 (all)
						GPIO_AFRL_AFSEL7_2);
	// Alternative function LOW register
	GPIOC->AFR[1] |= (	GPIO_AFRH_AFSEL8_2 |	// AF4 (all)
						GPIO_AFRH_AFSEL9_2 | 	// TODO: debug pin mod: PC9: remove test for tim 8 CCR4 (see other, and change back to EEPROM)
						GPIO_AFRH_AFSEL10_2 |
						GPIO_AFRH_AFSEL11_2 |
						GPIO_AFRH_AFSEL12_2);

This is the deactivation:

CLEAR_BIT(TIM8->CCER, TIM_CCER_CC1E | TIM_CCER_CC2E | TIM_CCER_CC3E);

Timer init:

void initTimer8PWM(){	// BOOKMARK |  initTimer8PWM
	__HAL_RCC_TIM8_CLK_ENABLE();		// Enable clock

	CLEAR_REG(TIM8->AF1);				// Disable BKIN input
	CLEAR_REG(TIM8->AF2);

	SET_BIT(TIM8->CR1, 	TIM_CR1_ARPE | 	// ARR register is bufferd
						TIM_CR1_CMS_1 	// center aligned up/down (Center-aligned mode 2). (interrupt on counting up only - for ADC trigger only?)
						);

	//TODO: check entries again for pwm
	SET_BIT(TIM8->CR2, 	TIM_CR2_MMS2_2 | TIM_CR2_MMS2_1 | TIM_CR2_MMS2_0);// tim_oc4refc rising edges generate pulses on tim_trgo2 for ADC trigger
	SET_BIT(TIM8->CR2, 	TIM_CR2_CCUS);			// Update on COM or trigger in

	//TIMx_ARR -1 ist max counter (Counter is counted up and down, so PWM has half the tics)
	WRITE_REG(TIM8->ARR, PWM_HALF_CYCLE_TICS); 	// Counter TOP
	WRITE_REG(TIM8->CCR4, ADC_TRIG_PRE_COUNT);	// compare value 4 (ADC trigger)


	TIM8->PSC = TIM_8_PSC - 1;

//	WRITE_REG(TIM8->CCR1, DUTY_TO_TICS(10));	// compare value 1
//	WRITE_REG(TIM8->CCR2, DUTY_TO_TICS(10));	// compare value 2
//	WRITE_REG(TIM8->CCR3, DUTY_TO_TICS(10));	// compare value 3


	// ***************************************************************
	// ****** ATTENTION! TIM CH 1 is PH 3 and CH 3 is PH 1 !!!  ******
	// ***************************************************************

	SET_BIT(TIM8->CCMR1, 	TIM_CCMR1_OC1M_2 | TIM_CCMR1_OC1M_1	| // pwm output compare polarity channel 1 and 2 (pwm mode 1)
							TIM_CCMR1_OC2M_2 | TIM_CCMR1_OC2M_1 |
							TIM_CCMR1_OC1PE  | TIM_CCMR1_OC2PE); 	// preload enable ccr 1 + 2
	// Default is OUTPUT !!!
	// CC1S = 0 > channel output (CC1 as OUTPUT)

	SET_BIT(TIM8->CCMR2, 	TIM_CCMR2_OC3M_2 | TIM_CCMR2_OC3M_1	| // pwm output compare polarity channel 3 and 4 (pwm mode 1)
							TIM_CCMR2_OC4M_2 | TIM_CCMR2_OC4M_1 |
							TIM_CCMR2_OC3PE  | TIM_CCMR2_OC4PE); 	// preload enable ccr 3 + 4



	// Timer 1 trigger out comes in on itr0 (Only trgo is possible!)
	//TIM8->SMCR itr0 is default 0!


	//TODO: debug remove ?? Really? its current calculation?
	SET_BIT(TIM8->CCER, TIM_CCER_CC4E);		// Enable output

	TIM8->DIER |= TIM_DIER_CC4IE;			// Enable interrupts (from ADC trigger) for kind of sine wave generation
	//TIM8->CR1 |= TIM_CR1_URS;	does it work with update from timer 1?// Only update interrupt on overflow and DMA TODO: does it work with interrupt


	SET_BIT(TIM8->BDTR, TIM_BDTR_OSSR); // inactive state high or low
	CLEAR_BIT(TIM8->CCER, TIM_CCER_CC1P);// oc1 polarity active high
	CLEAR_BIT(TIM8->CCER, TIM_CCER_CC2P);// oc2 polarity active high
	CLEAR_BIT(TIM8->CCER, TIM_CCER_CC3P);// oc3 polarity active high
	// Polarity ONLY for pins, has no effect on trigger lines!!!
}

void startTimer8(){
	__disable_irq();

	SET_BIT(TIM8->EGR , 1);				// Send event, to load all register via Update event (UG)

	SET_BIT(TIM8->CR1, TIM_CR1_CEN); 	// Counter enable
	switchToSectorOFF();				// Dont drive any outputs yet!
	SET_BIT(TIM8->BDTR, TIM_BDTR_MOE); 	// Connect signals to outputs (When CCxE and CCxNE are set - see also OSSR and OSSI)
	WRITE_REG(TIM8->SR, 0); 			// Clear any int flags
	__enable_irq();
}

I believe this was causing me the headache i had when blowing mosfets and having to change chips.

Is there a way to have the output not floating?

[TDK]

> i found out, that the output is floating, when it is not activated to output the PWM signal of timer 8.

> Is there a way to have the output not floating?

If you want a specified state when the chip is in reset, an external pullup is needed. Otherwise, you can configure the pin with an internal pullup which gets activated when the program runs.

You can see the output states of pins when MOE=1 in this table. Choose one in which they're not floating.