1-Wire

1-Wire is a wired half-duplex serial bus designed by Dallas Semiconductor that provides low-speed (16.3 kbit/s[1]) data communication and supply voltage over a single conductor.

It is typically used to communicate with small inexpensive devices such as digital thermometers and weather instruments.

Manufacturers also produce devices more complex than a single component that use the 1-Wire bus to communicate.

Examples include temperature loggers, timers, voltage and current sensors, battery monitors, and memory.

USB, RS-232 serial, and parallel port interfaces are popular solutions for connecting a MicroLan to the host PC.

iButtons are connected to 1-Wire bus systems by means of sockets with contacts that touch the "lid" and "base" of the canister.

Some uses include locks, burglar alarms, computer systems, manufacturer-approved accessories, time clocks and courier and maintenance keys for smart safes.

Despite the "1-Wire" name, all devices must also have a second conductor for a ground connection to permit a return current to flow through the data wire.

[5] Communication occurs when a master or slave briefly pulls the bus low, i.e., connects the pull-up resistor to ground through its output MOSFET.

The data wire is high when idle, and so it can also power a limited number of slave devices.

The master starts a transmission with a reset pulse, which pulls the wire to 0 volts for at least 480 μs.

The falling (negative) edge of the pulse is used to start a monostable multivibrator in the slave device.

When receiving data, the master sends a 1–15 μs 0 volt pulse to start each bit.

The basic sequence is a reset pulse followed by an eight-bit command, and then data are sent or received in groups of eight bits.

The master uses this simple behavior to search systematically for valid sequences of address bits.

The 56-bit address space is searched as a binary tree, allowing up to 75 devices to be found per second.

For these situations, a microcontroller can use several pins, or the manufacturer has a 1-Wire device that can switch the bus off or pass it on.

[7] The following signals were generated by an FPGA, which was the master for the communication with a DS2432 (EEPROM) chip, and measured with a logic analyzer.