transferred ow module documentation
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# onewire Module
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## ow.check_crc16()
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Compute the 1-Wire CRC16 and compare it against the received CRC.
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####Syntax
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`ow.check_crc16(buf, inverted_crc0, inverted_crc1[, crc])`
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#### Parameters
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- `buf` string value, data to be calculated check sum in string
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- `inverted_crc0` LSB of received CRC
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- `inverted_crc1` MSB of received CRC
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- `crc` CRC starting value (optional)
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#### Returns
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`bool` true, if the CRC matches; false for mismatch.
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## ow.crc16()
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Compute a Dallas Semiconductor 16 bit CRC. This is required to check the integrity of data received from many 1-Wire devices. Note that the CRC computed here is **not** what you'll get from the 1-Wire network, for two reasons:
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1. The CRC is transmitted bitwise inverted.
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2. Depending on the endian-ness of your processor, the binary representation of the two-byte return value may have a different byte order than the two bytes you get from 1-Wire.
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#### Syntax
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`ow.crc16(buf[, crc])`
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#### Parameters
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- `buf` string value, data to be calculated check sum in string.
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- `crc` CRC starting value (optional)
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#### Returns
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`crc16` the CRC16, as defined by Dallas Semiconductor.
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## ow.crc8()
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Compute a Dallas Semiconductor 8 bit CRC, these are used in the ROM and scratchpad registers.
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#### Syntax
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`ow.crc8(buf)`
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#### Parameters
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`buf` string value, data to be calculated check sum in string.
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#### Returns
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CRC result as byte.
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## ow.depower()
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Stop forcing power onto the bus. You only need to do this if you used the 'power' flag to `ow.write()` or used a `ow.write_bytes()` and aren't about to do another read or write.
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#### Syntax
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`ow.depower(pin)`
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#### Parameters
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`pin` 1~12, IO index
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#### Returns
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`nil`
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####See also
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- [ow.write()](#owwrite)
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- [ow.write_bytes()](#owwrite_bytes)
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## ow.read()
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Read a byte.
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####Syntax
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`ow.read(pin)`
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#### Parameters
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`pin` 1~12, IO index
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#### Returns
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Byte read from slave device.
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## ow.read_bytes()
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Read multi bytes.
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#### Syntax
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`ow.read_bytes(pin, size)`
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#### Parameters
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- `pin` 1~12, IO index
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- `size` number of bytes to be read from slave device
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#### Returns
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`string` bytes read from slave device
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## ow.reset_search()
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Clear the search state so that it will start from the beginning again.
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#### Syntax
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`ow.reset_search(pin)`
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#### Parameters
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`pin` 1~12, IO index
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#### Returns
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`nil`
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## ow.search()
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Look for the next device.
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#### Syntax
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`ow.search(pin)`
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#### Parameters
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`pin` 1~12, IO index
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#### Returns
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`rom_code` string with length of 8 upon success. It contains the rom code of slave device. Returns `nil` if search was unsuccessful.
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#### See also
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[ow.target_search()](#owtargetsearch)
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## ow.select()
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Issue a 1-Wire rom select command, make sure you do the `ow.reset(pin)` first.
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#### Syntax
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`ow.select(pin, rom)`
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#### Parameters
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- `pin` 1~12, IO index
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- `rom` string value, len 8, rom code of the salve device
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#### Returns
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`nil`
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#### Example
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```lua
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-- 18b20 Example
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pin = 9
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ow.setup(pin)
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count = 0
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repeat
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count = count + 1
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addr = ow.reset_search(pin)
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addr = ow.search(pin)
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tmr.wdclr()
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until (addr ~= nil) or (count > 100)
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if addr == nil then
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print("No more addresses.")
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else
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print(addr:byte(1,8))
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crc = ow.crc8(string.sub(addr,1,7))
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if crc == addr:byte(8) then
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if (addr:byte(1) == 0x10) or (addr:byte(1) == 0x28) then
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print("Device is a DS18S20 family device.")
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repeat
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ow.reset(pin)
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ow.select(pin, addr)
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ow.write(pin, 0x44, 1)
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tmr.delay(1000000)
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present = ow.reset(pin)
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ow.select(pin, addr)
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ow.write(pin,0xBE,1)
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print("P="..present)
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data = nil
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data = string.char(ow.read(pin))
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for i = 1, 8 do
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data = data .. string.char(ow.read(pin))
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end
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print(data:byte(1,9))
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crc = ow.crc8(string.sub(data,1,8))
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print("CRC="..crc)
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if crc == data:byte(9) then
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t = (data:byte(1) + data:byte(2) * 256) * 625
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t1 = t / 10000
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t2 = t % 10000
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print("Temperature="..t1.."."..t2.."Centigrade")
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end
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tmr.wdclr()
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until false
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else
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print("Device family is not recognized.")
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end
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else
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print("CRC is not valid!")
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end
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end
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```
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####See also
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[ow.reset()](#owreset)
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## ow.setup()
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Set a pin in onewire mode.
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#### Syntax
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`ow.setup(pin)`
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#### Parameters
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`pin` 1~12, IO index
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#### Returns
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`nil`
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## ow.reset()
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Perform a 1-Wire reset cycle.
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#### Syntax
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`ow.reset(pin)`
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#### Parameters
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`pin` 1~12, IO index
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#### Returns
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- `1` if a device responds with a presence pulse.
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- `0` if there is no device or the bus is shorted or otherwise held low for more than 250 µS.
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## ow.skip()
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Issue a 1-Wire rom skip command, to address all on bus.
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#### Syntax
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`ow.skip(pin)`
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#### Parameters
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`pin` 1~12, IO index
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#### Returns
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`nil`
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## ow.target_search()
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Set up the search to find the device type `family_code` on the next call to `ow.search()` if it is present.
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#### Syntax
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`ow.target_search(pin, family_code)`
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#### Parameters
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- `pin` 1~12, IO index
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- `family_code` byte for family code
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#### Returns
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`nil`
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####See also
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[ow.search()](#owsearch)
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## ow.write()
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Write a byte. If `power` is 1 then the wire is held high at the end for parasitically powered devices. You are responsible for eventually depowering it by calling `ow.depower()` or doing another read or write.
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#### Syntax
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`ow.write(pin, v, power)`
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#### Parameters
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- `pin` 1~12, IO index
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- `v` byte to be written to salve device
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- `power` 1 for wire being held high for parasitically powered devices
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#### Returns
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`nil`
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####See also
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[ow.depower()](#owdepower)
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## ow.write_bytes()
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Write multi bytes. If `power` is 1 then the wire is held high at the end for parasitically powered devices. You are responsible for eventually depowering it by calling `ow.depower()` or doing another read or write.
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#### Syntax
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`ow.write_bytes(pin, buf, power)`
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#### Parameters
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- `pin` 1~12, IO index
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- `buf` string to be written to slave device
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- `power` 1 for wire being held high for parasitically powered devices
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#### Returns
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`nil`
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####See also
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[ow.depower()](#owdepower)
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@ -43,9 +43,10 @@ pages:
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- 'http': 'en/modules/http.md'
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- 'hx711' : 'en/modules/hx711.md'
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- 'i2c' : 'en/modules/i2c.md'
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- 'mqtt': 'en/modules/mqtt.md'
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- 'net': 'en/modules/net.md'
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- 'node': 'en/modules/node.md'
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- 'mqtt': 'en/modules/mqtt.md'
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- 'ow': 'en/modules/ow.md'
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- 'pwm' : 'en/modules/pwm.md'
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- 'rtcmem': 'en/modules/rtcmem.md'
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- 'rtctime': 'en/modules/rtctime.md'
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