Working with STM32F7 and Timers: Output Compare Mode

In the previous guide (here), we took a look at the PWM mode in timer2 of STM32F767. In this guide, we shall take a look at the output compare where the the output will be toggled each time the timer overflow.

In this guide we cover the following:

• What is output compare mode
• Required parts and connection
• Code
• Demo

1. What is output compare mode:

In this mode, the timer shall count to the maximum level (set by the ARR), the following will happen:

• Assigns the corresponding output pin to a programmable value defined by the output compare mode.
• Sets a flag in the interrupt status register.
• Generates an interrupt if the corresponding interrupt mask is set.
• Sends a DMA request if the corresponding enable bit is set.

In our case, we will toggle PA5 (TIM2_CH1) based on out setting.

2. Required parts:

We will need the following:

• STM32F767 Nucleo-64
• LED
• Breadboard
• Hookup wires

3. Code:

We start of by enabling clock access to GPIOA and set PA0 to alternative function as shown in PWM guide:

#define TIM2_AF 0x01
	RCC->AHB1ENR	|=	RCC_AHB1ENR_GPIOAEN;
	GPIOA->MODER&=~	GPIO_MODER_MODER0; //reset PA0 and PA1
	GPIOA->MODER|=	GPIO_MODER_MODER0_1; //set PA0 and PA1 as alternate mode
	GPIOA->AFR[0] |= (TIM2_AF<<0); 

Then enable clock access to timer2 and disable the timer

	RCC->APB1ENR  |=  RCC_APB1ENR_TIM2EN;
	TIM2->CR1     &=~ TIM_CR1_CEN;

Then we need to set the pin to toggle on match in CCRM1 register:

TIM2->CCMR1|=TIM_CCMR1_OC1M_0|TIM_CCMR1_OC1M_1;

Then enable channel1 from capture/compare enable register

TIM2->CCER|=TIM_CCER_CC1E;

Since the MCU is running at 16MHz we can achieve toggle rate of 1Hz by setting the prescaler to 15999 and ARR to 1000 as following:

	TIM2->PSC=16000-1; /*16 000 000 / 16 000 =1 000*/
	TIM2->ARR=1000-1; /*1 000 / 1 000 = 1HZ*/

Finally enable the timer

TIM2->CR1     |= TIM_CR1_CEN;

4. Demo:

And we are successfully blinked the LED with rate of 1Hz using the hardware level rather than forcing the MCU to wait or generating an interrupt

Happy coding 🙂