1 Theory of Operation - Maxim’s 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 host/target scheme. One or several target devices can be connected to the bus at the same time, but only one host should be connected to the bus.

The bus is idle high, so a pull-up resistor is necessary. To determine the value of the pull-up resistor, refer to the data sheet of the target 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. Target devices are allowed to have a time base that differs significantly from the nominal time base. This, however, requires the timing of the host to be very accurate to ensure correct communication with target devices with different time bases. It is, therefore, very important to obey the time limits described in the following sections.