August 20, 2016 by zafer mehmood95

Filed under Power Over Ethernet Poe

Last modified August 20, 2016


1-Wire is a device communication bus system designed by Dallas Semiconductor Corp. that low-speed data features, signaling, and power over a single signal. 1-Wire is similar in concept to I²C, but at lower data rates and greater range. It is usually used to communicate with small inexpensive devices Such digital thermometers and weather instruments. A network of 1-Wire devices with an associated master device called a Micro lab.
Typically, the bus is possible with only two wires: data and ground. In order to achieve this, 1-Wire devices are, inter alia, to store an 800 pF capacitor charge, and to power the device during periods in which the data line is active.
Use example
Depending on the function, native 1-Wire devices are as separate components in an integrated circuit and TO92 packaging, and in some cases, referred to as a portable iButton format that resembles a watch battery. Manufacturers also produce devices more complex than one component that communicates the 1-Wire bus.
1-Wire devices can be one of many components on a printed circuit board in a product, a single component may in a device such as a temperature probe, or can be attached to a device is monitored. Some laboratories and other data acquisition and connected to control 1-Wire devices using cables with modular connectors, or CAT-5 cable, with the devices mounted in a socket, use a small PCB, or attached to the object being checked. In such systems, RJ11 (6P2C or 6P4C modular connector, commonly used for telephones) are popular.
Systems of sensors and actuators can be constructed by 1-Wire wiring components with each other. Each component contains all the necessary logic to the 1-Wire bus. Examples include temperature logger, timers, voltage and current sensors, battery monitors, and memory. These can be connected to a computer via a bus converter. USB, RS-232 serial and parallel port interfaces are popular solutions for the connection of the Microloan the host PC. 1-Wire devices can also be connected directly to microcontrollers from different vendors.
The iButton (also known as the Dallas Key) is a mechanical packing standard which places a 1-Wire component in a small stainless steel “button” is similar to a disc-shaped watch battery. iButtons to get connected to 1-Wire bus systems through sockets with contacts of the bus the “lid” and the “base”. Alternatively, the compound can be semi-permanently with a socket to be in the iButton clips, but is easy to remove from.
The Java Ring, ring mounted iButton with a Java Virtual Machine compatible with the Java Card 2.0 specification inside, was given to the participants of the conference 1998JavaOne.
Each 1-Wire chip has a unique ID code. This feature makes the chips, in particular in an iButton package, suitable for use as a key to open a lock, deactivation arm, and burglar alarms, authenticate computer users of the system, working time clock systems, have etc. iButtons used as Akbil smart tickets for public transport in Istanbul.
Dell power
Genuine use Dell laptop power supplies 1-Wire protocol to send data through the third wire to the laptop (about power, current and voltage ratings). The laptop will refuse to charge if the adapter does not meet requirements.
Communication protocol
In each Microloan, there is always a great overall control, which can be a PC or a microcontroller. The master initiates the activity on the bus, facilitates avoiding collisions on the bus. Protocols are built into the software to detect collisions. After a collision, the master retries the necessary communications.
Many devices can share the same bus. Each device on the bus has a unique 64-bit serial number. The least significant byte of the serial number is an 8-bit number that tells the type of the device. The most significant byte is a standard (for a 1-wire bus) 8-bit CRC.
There are several standard broadcast commands and commands used to address a particular device. The master can select a command, then send the address of a particular device. The following command is executed only by the recipient device.
The 1-wire bus enumeration protocol (described later), such as other singulation protocols, is an algorithm used for the master reads the address of each device on the bus. Since the address includes the device type, and CRC, recovering the address grid also produces a reliable overview of the devices on the bus. The 64-bit address space is searched as a binary tree, thereby to obtain up to 75 devices per second.
The Dallas 1-Wire network physically implemented as an open drain master device connected to one or more open drain slaves. A pull-up resistance is for all of the devices and operates to pull the bus to 3 and 5 volts, and can supply power to the slave device. Communication takes place when a master or slave asserts the bus is low, i.e., connects the pull-up resistor to the ground by means of its power MOSFET. Specific 1-Wire driver and bridge chips are also available. Data rates of 16.3 kbit / s can be achieved. There is also an overdrive mode, which speeds up the communication with a factor of 10.
The master starts a transmission with a reset pulse, which pulls the wire to 0 volts for at least 480 microseconds. Displays all slave device on the bus. Then each slave device, if present, it appears that there is a “presence” pulse: it keeps the bus from at least 60 microseconds after the master releases the bus.
To send a “1”, the bus master sends a very short (1-15 ps) low heart rate. To transmit a “0”, the master sends a 60-microsecond low pulse. The downward (negative) end of the pulse is used to initiate a monostable multi-vibrator in the slave device. The multi-vibrator in the slave clocks to the data line read approximately 30 ps after the falling edge. multivibrator slave inevitably analog tolerances that the timing accuracy, which is why the “0” pulses 60 microseconds long his influence, and the “1” pulses can not be longer than 15 microseconds.
When a special one-wire interface peripheral is not available, a UART can be used to perform a 1-wire bus master. Serial or USB “bridge” chips are also available that the timing and waveform requirements of the 1-Wire bus, and are particularly useful when utilizing a long (more than 100 m) cables. Up to 300 meters long buses consisting tested from simple twisted pair telephone cable manufacturer. However, it will adjustment of pull-up resistors require 5-1 kQ.
When receiving data, the master sends a 1-15-ps 0 volt pulse to start at each bit. If transmission slave unit wants to send a “1”, does nothing, and the bus goes to the extended voltage? If the sending slave wants to send a “0”, the data line goes to ground for 60 microseconds.
The base sequence followed by a reset pulse is sent or received an 8-bit instruction and data in groups of 8 bits.
When a series of data being transferred, errors can be detected by an 8-bit CRC (weak data).
To find the devices, the master sends a list command and an address, “listen” after every bit of an address. If a slave has all address bits so far, is the result of a 0. The master uses this simple behavior systematic search for valid sequences of address bits. The process is much faster than a brute force search for all possible 64-bit numbers because as soon as an invalid bit is detected, all subsequent address bits known invalid. A list of up to 15 devices 10 ends up rapidly.
The location of devices on the bus at times significantly. For these situations, the manufacturer has a special device that is either by bus or switches it off. The software can then explore sequential bus domains.

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