Introduction

The 1-Wire® protocol, sometimes referred to as Dallas 1-Wire or simply one-wire, is probably the most widely known form of one-wire half-duplex serial communication. However, 1-Wire is not the only form of half-duplex serial communication over a single wire.

Using a single wire for communication can sometimes reduce the total cost of a product, whereas using multiple wires for serial communication would force a change to a higher pin count device.

In this document, the term 1-Wire refers exclusively to the 1-Wire protocol. The term one-wire refers to any form of one-wire half-duplex communication including, but not limited, to the Dallas 1-Wire protocol.

In order to communicate over one-wire with a Universal Synchronous Asynchronous Receiver Transmitter (USART), an open-drain or open-collector circuit is needed. Older AVR® devices require external components and two pins to achieve this. On the new tinyAVR® 0- and 1-series and megaAVR® 0-series, one pin is enough and no external components are needed. Before looking more closely at the old and new solution, some background information about half duplex and open-drain is provided.