What Is The 1-Wire Net?

The 1-Wire® Net, previously known as the MicroLAN, is a low-cost network based on a PC or microcontroller communicating digitally over twisted-pair cable with 1-Wire components. The network is defined with an open drain (wired-AND) master/slave multidrop architecture that uses a resistor pull-up to a nominal 5-volt supply at the master. A 1-Wire Net-based system consists of three main elements: a bus master with controlling software, the wiring and associated connectors, and 1-Wire devices. Any standard microcontroller such as an 8051 with at least a 1.8MHz clock, as well as a PC using a 115.2 kbps-capable UART, can serve as master for the Net.

1-Wire Net protocol uses conventional CMOS/TTL logic levels, where 0.8V or less indicates a logic zero and 2.2V or greater represents a logic one. Operation is specified over a supply voltage range of 2.8 to 6 volts. Both the master and slaves are configured as transceivers allowing data to flow in either direction, but only in one direction at a time. Technically speaking, data transfers are half-duplex and bit-sequential over a single pair of wires, data and return, from which the slaves "steal" power by use of an internal diode and capacitor. Data is read and written least significant bit first. An economical DS9097 COM Port Adapter is available to interface RS-232 to the net. Newer, more versatile, adapters based on the DS2480B Serial 1-Wire Line Driver chip provide more capability such as active pull-up and slew-rate control. The DS2480B is designed to interface between RS-232 and the 1-Wire bus, generating the proper signals and programmable waveforms that provide maximum performance. Regardless of whether a DS9097- or DS2480B-based adapter is used, readily available, low-capacitance, unshielded, Category 5 twisted pair phone wire is recommended for the bus.