STM32 encoder interface mode

1. Encoder

Figure 1 Encoder schematic diagram 

Figure 1 is a schematic diagram of the encoder. In the middle is a code disk with a grating. When light passes through the grating, the receiving tube receives a high level. If light does not pass through, it receives a low level. When the motor rotates one circle, the number of gratings on the code disk is equal to the number of high levels received by the receiving tube.

2.stm32 encoder interface mode (register)

The encoder interface mode of STM32 is described in detail in the STM32 Chinese reference manual. 

Figure 2 STM chip encoder interface mode description 

The following figure is an example of a counter operation, showing the generation and direction control of the count signal. It also shows how input jitter is suppressed when both edges are selected; jitter can occur when the sensor is positioned close to a transition point. In this example, we assume the following configuration: 

Figure 3 Example of counter operation in encoder mode 

When the TI 1 waveform precedes the TI 2 waveform by 90°, the counter increases by 1 each time the edge changes (addition and subtraction can be set by registers). It can be seen that one raster is counted 4 times. When the TI 1 waveform lags behind the TI 2 waveform by 90°, the counter decreases by 1 each time an edge changes.

1.  //TIM2_Encoder_Init,Tim2_CH1(PA0);Tim2_CH2(PA1)

2. //arr: automatically reload value 0XFFFF

3. //psc: clock pre-division number, no division

4.  void TIM2_Encoder_Init(u16 arr,u16 psc)

5.  {

6. RCC->APB1ENR|=1<<0; //TIM2 clock enable

7. RCC->APB2ENR|=1<<2; //Enable PORTA clock

8.          

9. GPIOA->CRL&=0XFFFFFF00; //PA0, PA1 clear previous settings

10. GPIOA->CRL|=0X00000044; //PA0, PA1 floating input

11.             

12. TIM2->ARR=arr; //Set the counter to automatically reload value 

13. TIM2->PSC=psc; //Prescaler

14. 

15. TIM2->CCMR1 |= 1<<0; //Input mode, IC1FP1 is mapped to TI1

16. TIM2->CCMR1 |= 1<<8; //Input mode, IC2FP2 is mapped to TI2

17. TIM2->CCER |= 0<<1; //IC1 does not reverse

18. TIM2->CCER |= 0<<5; //IC2 does not reverse

19. TIM2->SMCR |= 3<<0; //All inputs are valid on the rising or falling edge

20. TIM2->CR1 |= 1<<0; //Enable counter

21. }