Understanding D1W
D1W is a one-wire bus. It is usually used for simple sensors (temperature or humidity) and has "buttons" that just show a unique identifier. This is an interesting bus where the power of the device can also come from the wire that is used to transmit data. This is usually not supported by hardware peripherals in MCUs; you need to bit-bang the protocol. Bit-banging a protocol means that we will implement the protocol manually by using the GPIOs of the blue pill. 1-Wire is an open-drain bus (like I2C or UART) and hence needs an external pullup resistor (usually of 5k ohms) to set the voltage to a known state when the MCU disconnects the pin (also called floating as in the code).
Mode of operation
The communication on the D1W is time-based and is initialized by sending a reset pulse that the slave will answer to (the presence pulse).
The reset pulse
The reset pulse is initialized by the master pulling low the data line for at least 480 µS.
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