can not read temp from ds18b20 - stm32

Question

I am using stm32 to read the ds18b20 with HAL library
I think the init is correct but the read and write is not
anyone can tell me why it is not right?
for the write,here is the code
if ((data & (1 << i)) != 0)
{
MX_GPIO_Set(1);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_1, GPIO_PIN_RESET);
delay_ms(1);
MX_GPIO_Set(0);
delay_ms(60);
}
else
{
MX_GPIO_Set(1);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_1, GPIO_PIN_RESET);
delay_ms(60);
MX_GPIO_Set(0);
}
it is write one bit data.
and for the read code
MX_GPIO_Set(1);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_1, GPIO_PIN_RESET);
delay_ms(2);
MX_GPIO_Set(0);
if (HAL_GPIO_ReadPin(GPIOA, GPIO_PIN_1) == GPIO_PIN_SET)
{
value |= 1 << i;
}
delay_ms(60);
the MX_GPIO_Set(1) means set the GPIO output
where is wrong?
please do not tell me use library or code in github.I want to write code myself so I can understand the ds18b20.

Answer 1

The DS18B20 uses the One-Wire protocol.
https://en.wikipedia.org/wiki/1-Wire
Each bit takes about 60 microseconds to transmit.
1s are HIGH during most of the transmission and 0s are LOW during most of the transmission. The start of the next bit is indicated by a pulse.
One thing that stands out to me is that you're using delay_ms (milliseconds), when you likely want to be using delay_us (microseconds).
Also, you're relying on the bit's timing to be exact (which it probably won't be). Instead, base your timing on the pulse.
It's more complicated than that.
When reading, you need to be continually checking the pin's value and interpreting what it means rather than putting in delays and hoping that the timing matches up.
I have not tested this code and it's incomplete.
This is just to illustrate a technique.
To start off, we're going to set our output to LOW and wait
for the sensor to go LOW for at least 200us. (Ideally 500us. 200us is our minimum requirement.)
This is the "RESET" sequence that tells us that new data is about to start.
const int SleepIntervalMircoseconds = 5;
// Start off by setting our output to LOW (aka GPIO_PIN_RESET).
MX_GPIO_Set(1);
HAL_GPIO_WritePin(GPIOA, GPIO_PIN_1, GPIO_PIN_RESET);
// Switch back to reading mode.
MX_GPIO_Set(0);
const int ResetRequiredMiroseconds = 200;
int pinState = GPIO_PIN_SET;
int resetElapsedMicroseconds = 0;
while (pinState != GPIO_PIN_RESET || resetElapsedMicroseconds < ResetRequiredMiroseconds) {
pinState = HAL_GPIO_ReadPin(GPIOA, GPIO_PIN_1);
if (pinState != GPIO_PIN_RESET) {
resetElapsedMicroseconds = 0;
continue;
}
delay_us(SleepIntervalMircoseconds);
// Note that the elapsed microseconds is really an estimate here.
// The actual elapsed time will be 5us + the amount of time it took to execute the code.
resetElapsedMicroseconds += SleepIntervalMircoseconds;
}
This only gets us started.
After you've received the reset signal, you need to indicate to the other side that you've received it by setting your value HIGH for certain amount of time.

Answer 2

I'm unable to comment on your code, because important parts like the GPIO setup and the source for the functions called are missing. However, if the bit timing gives you trouble, you might try this.
Using a UART to Implement a 1-Wire Bus Master
then you don't have to deal with delays and timings other than calculating the UART baud rate.
All STM32 UARTs support one wire operation with an open drain GPIO pin. Connect the I/O pin of the device to an UART TX pin. Configure the pin as open-drain alternate function output, with the alternate function number for the UART if applicable. Enable the UART and set it to single wire operation in the control registers.
Set the UART baud rate to 7407, and send 0xF0, that's the reset pulse. Wait for RXNE and read the UART data register. If it's not 0xF0, then the device is answering with a presence pulse.
Set the UART baud rate to 133333, and you can start communicating. To send a 0 bit, write 0x00 to the UART data register. To send a 1 bit, write 0xFF to the UART data register. To receive a bit, write 0xFF, wait for RXNE, and read the data register. If the byte read is 0xFF, then it's a 1, otherwise (any other value read) it's a 0.