Read ds18b20 from stm32f103 under stm32cubemx

environment:

AND 7.4

stm32cubemx 4.13.1

stm32f1 1.3.1

freertos 8.1

Reading ds18b20 is mainly about timing, which is a microsecond delay.

Let’s look at the circuit first:

A pull-up resistor is used here, and DQ is set to OD mode. When reading and outputting, the direction of the PIN is changed. If no change is made, only a value of 0 can be read. 

If you do not want to use pull-up resistors, you can set DQ to PP mode, which the Mbed development board can successfully read out.

Code without circuits is incomplete and difficult to understand.

The delay is implemented by using a timer or a nop instruction. Here, Timer3 is used to provide ticks.

The configuration of GPIO and TIMER uses stm32cubemx, which is not listed here. If you have any questions, you can ask them in the forum .

1. /* 

2. * Microsecond delay 

3. */  

4. void therm_delay(uint16_t nCount)  

5. {  

6.   __IO uint16_t TIMCounter = nCount;  

7.     

8.   uint16_t start = TIM_MST->CNT;  

9.   uint16_t end = start + TIMCounter;  

10.   __IO uint16_t read;  

11.     

12.   while (1) {  

13.     read = TIM_MST->CNT;  

14.     if(read < start)  

15.       read = 0xffff - start + read;  

16.     if (read >= end)  

17.       break;  

18.   }  

19.     

20. }  

Frequently called change directions and reads are changed to register operations to reduce the overhead of function calls. 

Modify the port and pin as needed.

1. //PB8: IO direction setting  

2. #define THERM_INPUT_MODE()  { GPIOB->CRH &= 0xFFFFFFF0; GPIOB->CRH |= 0x4; }  

3. #define THERM_OUTPUT_MODE() { GPIOB->CRH &= 0xFFFFFFF0; GPIOB->CRH |= 0x5; }  

4.   

5. #define DQ_READ() ((GPIOB->IDR & GPIO_PIN_8) >> 8)  

Putting the reading of ds18b20 in a task that does not require high real-time performance will delay the execution of the task by several milliseconds.

There is CRC verification in the code. If an interrupt or other task interferes with the reading timing, the value will be thrown away when it is retrieved. Therefore, you can integrate it into your own project with confidence.

transfer:

1. // Read the result  

2. typedef struct {  

3.   int8_t value;  

4.   int8_t error;  

5. } ThermValue;  

6. .  

7. .  

8. .  

9. __IO ThermValue v_ds18b20;  

10. /* ds18b20 */  

11. if (start_conversion) {  

12.   v_ds18b20 = therm_read_temperature();  

13.   start_conversion = false;  

14. }  

15. else {  

16.   therm_start_conversion();  

17.   start_conversion = true;  

18. }  

19. if (v_ds18b20.error == 0)  

20.   cv = v_ds18b20.value;  

There are a lot of codes and examples for operating ds18b20, which are actually very simple, but some codes work normally for others but not for me. 

The reason is the inconsistency between hardware and software, and there is nowhere to turn when problems occur.