1 Theory of Operation - The Dallas 1-Wire® Protocol

A 1-Wire bus uses only one wire for signaling and power. Communication is asynchronous and half-duplex, and it follows a strict master/slave scheme. One or several slave devices can be connected to the bus at the same time. Only one master should be connected to the bus.

The bus is idle high, so there must be a pull-up resistor present. To determine the value of the pull-up resistor, see the data sheet of the slave device(s). All devices connected to the bus must be able to drive the bus low. An open-collector or open-drain buffer is required if a device is connected through a pin that can not be put in a tri-state mode.

Signaling on the 1-Wire bus is divided into time slots of 60 μs. One data bit is transmitted on the bus per time slot. Slave devices are allowed to have a time base that differs significantly from the nominal time base. This, however, requires the timing of the master to be very precise to ensure correct communication with slaves with different time bases. It is, therefore, very important to obey the time limits described in the following sections.