OneWire
The 1-Wire protocol is a low-speed half-duplex proprietary communication protocol. Requiring two lines, one for data/power and one for ground, or three in conventional mode when the data and power lines are separate, 1-Wire is capable of transmitting up to 200 meters at speeds of up to 16.3 kbps. 1-Wire chips store a unique 64-bit ID code in their ROMs and are commonly used for low-powered data storage or authentication.
Transmission
1-Wire communication is driven by a Master which initiates communication with up to 100 slaves. The nodes are connected to the Master by open-drain lines, which are high and brought low by connected devices to communicate in pulsed low signals of standardized lengths.
Communication Diagram
Signaling
In 1-Wire communication there is no clock signal to synchronize the devices, instead signals depend on communication states and timing. A 1 bit is defined as a period where the data line is held low for 1-15 μs, while a 0 bit is when the line is low for 60 μs. A Master device initiates communication with a slave device by sending a Reset Pulse where the line is pulled low for 480 μs. The slave responds to this with a Presence Pulse, holding the line low for 60 μs.
To read a bit from the slave device, the master pulls the line low for 1-15 μs then releases it, allowing the slave device to pull it low, or do nothing. If it pulls the line low for 60 μs, the Master reads a 0 bit, else it reads a 1.