1-wire technology

Тechnology 1-wire is not new and has been known for about 10 years. 1-wire is widely used in household and industrial systems. However, few people know about it. We are interested in the use of 1-wire systems automation. 1-wire is a network that can connect a variety of devices such as sensors (temperature, humidity, light), actuating keys, meters, readers, and more. All devices are linked together in the simplest case of two leading cable. One wire is used for data (hence the name “1-wire”), and the second wire – turning or “Earth”. Network topology – the total tire. This means that one cable goes through all devices. Branch permissible but not recommended (50 cm). However, for small networks of arbitrary topology is possible, for example, a star. The big advantage of 1-wire is that many, but not all, components 1-wire can do without external power, working on the so-called parasitic power, taking power from the data bus. However, low requirements for environmental data imposes some limits on speed. Thus, the maximum data rate for 1-wire technology normally is 15.4 kbit / s (up to 125 Kbit mode Overdrive). It seems to be quite slow, but given that the network is not transmitted by media as well, such as command keys and short answers sensors, it becomes clear that this is enough. To control the errors in the 1-wire protocol supports a checksum of incoming packets – CRC.

1wire

Advantages of 1-wire:

– Plain and simple network architecture
– Low requirements for cables
– The great length line
– Low cost and ease of components
– Open protocol and affordable software programming
– Ability to do in certain situations without power

Disadvantages of 1-wire:

– Low data rate
– Mandatory presence masters, a leading network

More details on the mandatory requirement of the presence masters network. The fact that the devices in terms of the exchange of data elements are passive circuit. 1-wire components can not be without a special request to send data to the network. Thus the device can not communicate with each other without the “active” leader. Elements of the network is always Powered. Master network 1-wire only one. He initiates, monitors and manages the network and networked devices. Depending on the software master 1-wire line can work differently with their wards, but it can eventually interviewed state a specific item, and send a request for a particular item of any information. For example, if we need a real-time display of the set temperature sensors, the master cycle network will take turns to interrogate these sensors. Reflect on the network can master only one device. As masters can act MC (microcontroller) that can, with appropriate software directly included in the 1-wire network via one of its input-output ports. Master can act as a PC (personal computer), which uses a combination of special items that allow you to connect 1-wire with COM-port or USB-port on your computer, such as the DS9097 or DS9490.
Також я вже писав раніше про взаємодію Arduino та Raspberry Pi із давачем температури DS18B20 по інтерфейсу 1-wire.

master

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