opkmen.blogg.se - Stm32 1 wire library

This MOSFET switching requires a not-that-simple control algorithm on a microcontroller (or similar).

A MOSFET is required to drive the DQ line to Vcc (bypassing the pull-up resistor) when the 1-wire device requires a high-current (such as writing to it's internal EEPROM, or performing a temperature measurement).

For reliable power over data communication, the data cannot have a too large sequence of zeros. To do this, the devices have an internal capacitor (usually 800pF), which stores energy from the data line when it goes high. To obtain true 1-wire communication (excluding ground), some 1-wire ICs support powering over the data line ( parasitic power). The 1-wire protocol has a unique discovery system in where the master can search and discover the addresses of all slaves on the bus, without knowing any information (like how slaves there are) beforehand. Part of this 64-bit address is an 8-bit family code, which identifies the device type/functionality. Image from AddressingĮach 1-wire slave device has a unique, unchangeable 64-bit ID which serves as it’s address on the 1-wire bus. The functional block diagram of the DS18B20 temperature sensor, showing the 1-wire interface circuitry.