OneWire总线基本点
One-wire总线是DALLAS公司研制开发的一种协议，采用单根信号线，既传输时钟，又传输数据而且数据传输是双向的。它具有节省I/O 口线资源、结构简单、成本低廉、便于总线扩展和维护等诸多优点。它由一个总线主节点､一个或多个从节点组成系统，通过一根信号线对从芯片进行数据的读取。每一个符合One-wire协议的从芯片都有一个唯一的地址，48位的序列号､8位的家族代码和8位的CRC代码。主芯片对各个从芯片的寻址依据这64位的不同来进行｡
One-wire总线利用一根线实现双向通信。因此其协议对时序的要求较严格，如应答等时序都有明确的时间要求。基本的时序包括复位及应答时序､写一位时序､读一位时序。在复位及应答时序中，主器件发出复位信号后，要求从器件在规定的时间内送回应答信号；在位读和位写时序中，主器件要在规定的时间内读回或写出数据。为了与其它模拟接口的子程序在结构形式上尽量一致，在One-wire模拟时序程序中把位读和位写时序拓延，形成低位在前的字节读写时序。最终形成三个子程序：复位及应答子程序､写N个字节子程序和读N个字节子程序。
1-wire 单总线适用于单个主机系统，能够控制一个或多个从机设备。主机可以是微控制器，从机可以是单总线器件，它们之间的数据交换只通过一条信号线。当只有一个从机位于总线上时系统可按照单节点系统操作；而当多个从机位于总线上，时则系统按照多节点系统操作。
OneWire的Arduino库函数
//用OneWire建立一个目标 myWire,对应一个特定引脚
OneWire myWire(pin)
Create the OneWire object, using a specific pin. Even though you can connect many 1 wire devices to the same pin, if you have a large number, smaller groups each on their own pin can help isolate wiring problems. You can create multiple OneWire objects, one for each pin.
//查询下一个设备，其地址用8字节数组addrArray表示
myWire.search(addrArray)
Search for the next device. The addrArray is an 8 byte array. If a device is found, addrArray is filled with the device's address and true is returned. If no more devices are found, false is returned.
Perform a search. If this function returns a '1' then it has enumerated the next device and you may retrieve the ROM from the OneWire_address variable. If there are no devices, no further devices, or something horrible happens in the middle of the enumeration then a 0 is returned. If a new device is found then its address is copied to newAddr. Use reset_search() to start over.
Return TRUE : device found, ROM number in ROM_NO buffer
FALSE : device not found, end of search
///开始一个新的查询
myWire.reset_search()
Begin a new search. The next use of search will begin at the first device.
You need to use this function to start a search again from the beginning.
You do not need to do it for the first search, though you could.
//复位
myWire.reset()
Reset the 1-wire bus. Usually this is needed before communicating with any device.
Perform a 1-Wire reset cycle. Returns 1 if a device responds with a presence pulse. Returns 0 if there is no device or the bus is shorted or otherwise held low for more than 250uS
Returns 1 if a device asserted a presence pulse, 0 otherwise.
//选择一个设备，对应的地址是addrArray
myWire.select(addrArray)
Do a ROM select. Select a device based on its address. After a reset, this is needed to choose which device you will use, and then all communication will be with that device, until another reset.
Issue a 1-Wire rom select command, you do the reset first.
//跳过设备选择，直接使用设备，适用于只有一个设备的情况
myWire.skip()
Skip the device selection. This only works if you have a single device, but you can avoid searching and use this to immediatly access your device.
Do a ROM skip，Issue a 1-Wire rom skip command, to address all on bus.
// Read a bit.读一个位
uint8_t read_bit(void);
Read a bit. Port and bit is used to cut lookup time and provide more certain timing.
// Read a byte.读一个字节
uint8_t read(void);
void read_bytes(uint8_t *buf, uint16_t count);
// Write a bit. 写一个位
void write_bit(uint8_t v);
Write a bit. Port and bit is used to cut lookup time and provide more certain timing.
The bus is always left powered at the end, see note in write() about that.
Stop forcing power onto the bus. You only need to do this if you used the 'power' flag to write() or used a write_bit() call and aren't about to do another read or write. You would rather not leave this powered if you don't have to, just in case someone shorts your bus.
// 写一个字节
myWire.write(num, 1);
void write(uint8_t v, uint8_t power = 0);
void write_bytes(const uint8_t *buf, uint16_t count, bool power = 0);
Write a byte, and leave power applied to the 1 wire bus.
The writing code uses the active drivers to raise the pin high, if you need power after the write (e.g. DS18S20 in parasite power mode) then set 'power' to 1, otherwise the pin will go tri-state at the end of the write to avoid heating in a short or other mishap.
//写一个字节
myWire.write(num);
Write a byte. If 'power' is one then the wire is held high at the end for parasitically powered devices. You are responsible for eventually depowering it by calling depower() or doing another read or write.
//进行CRC检查
myWire.crc8(dataArray, length)
uint8_t OneWire::crc8( uint8_t *addr, uint8_t len)
uint16_t OneWire::crc16(uint8_t* input, uint16_t len)
Compute a CRC check on an array of data.
Compute a Dallas Semiconductor 8 bit CRC. These show up in the ROM and the registers.
