1-Wire is a device communications bus system which provides data, signaling, and power over a single conductor. It is similar in concept to I²C, but with lower data rates and longer range. It is typically used to communicate with small inexpensive devices such as digital thermometers and weather instruments.
Note: 1-Wire is not suitable for low power hosts which rely on energy harvesting.
The UX2-1IS pin variant includes a 1-Wire interface:
The 1-Wire interface actually comprises of two wires, 1W (data and power) and GND:
| UX2 | Slave |
|---|---|
 |
1-Wire (data/power) |
 |
GND |
Slaves often operate at either 3V or 5V; you might require a voltage level translator (see App Note 4477 on manufacturer website for details).
1-Wire facilitates several wiring topologies as summarised below. In many cases, a shielded CAT5 network cable will be suitable, especially for long distance networks (up to 100m).
Note:
There are different electrical characteristics for each topology which can impair reliability if not properly managed (see Tutorual 148 on the manufacturer website for details).
The linear topology has a main cable which stretches from the master to the farthest slave (sensor). Additional slaves are connected along the main cable, often by short stretches of wire:
The stubbed topology is similar to linear, but intermediate slaves are connected to the main wire by longer cables (usually with lengths in excess of 3m):
The star topology has slaves connected by cables to a central point:
It is also possible to create switched topologies, where different branches of slaves can be enabled or disabled via a switch in the 1-Wire cable.
Because the 1W pin is held high for most of the time, and slave devices will often parasitically leach power from it, the 1-Wire interface is not suitable for hosts which rely on energy harvesting.
It is strongly advised to use an MCU or FPGA which has hardware support for 1-Wire. Alternatively, there are dedicated 1-Wire driver ICs available from the manufacturer. For more details, please see App Note 4206 on the manufacturer website.
If the end-user is using both the 1-Wire and UEXT interfaces at the same time, the UEXT connector will consume the GND pin. As such, it's recommended to have an additional GND pin to the left of the 1W pin.