269 lines
6.5 KiB
Markdown
269 lines
6.5 KiB
Markdown
# 1-Wire Module
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| Since | Origin / Contributor | Maintainer | Source |
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| :----- | :-------------------- | :---------- | :------ |
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| 2014-12-22 | [Zeroday](https://github.com/funshine) | [Zeroday](https://github.com/funshine) | [ow.c](../../app/modules/ow.c)|
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This module provides functions to work with the [1-Wire](https://en.wikipedia.org/wiki/1-Wire) device communications bus system.
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## ow.check_crc16()
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Computes 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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true if the CRC matches, false otherwise
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## ow.crc16()
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Computes 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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the CRC16 as defined by Dallas Semiconductor
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## ow.crc8()
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Computes 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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Stops 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, I/O 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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Reads 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, I/O 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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Reads 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, I/O index
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- `size` number of bytes to be read from slave device (up to 256)
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#### Returns
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`string` bytes read from slave device
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## ow.reset()
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Performs 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, I/O 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.reset_search()
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Clears 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, I/O index
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#### Returns
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`nil`
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## ow.search()
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Looks 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, I/O 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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Issues 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, I/O index
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- `rom` string value, len 8, rom code of the slave 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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-- 18b20 Example
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pin = 3
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ow.setup(pin)
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addr = ow.reset_search(pin)
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addr = ow.search(pin)
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if addr == nil then
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print("No device detected.")
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else
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print(addr:byte(1,8))
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local 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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tmr.create():alarm(1000, tmr.ALARM_AUTO, function()
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ow.reset(pin)
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ow.select(pin, addr)
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ow.write(pin, 0x44, 1) -- convert T command
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tmr.create():alarm(750, tmr.ALARM_SINGLE, function()
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ow.reset(pin)
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ow.select(pin, addr)
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ow.write(pin,0xBE,1) -- read scratchpad command
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local data = ow.read_bytes(pin, 9)
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print(data:byte(1,9))
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local 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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local t = (data:byte(1) + data:byte(2) * 256) * 625
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local sgn = t<0 and -1 or 1
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local tA = sgn*t
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local t1 = math.floor(tA / 10000)
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local t2 = tA % 10000
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print("Temperature="..(sgn<0 and "-" or "")..t1.."."..t2.." Centigrade")
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end
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end)
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end)
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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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Sets 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, I/O index
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#### Returns
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`nil`
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## ow.skip()
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Issues 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, I/O index
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#### Returns
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`nil`
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## ow.target_search()
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Sets up the search to find the device type `family_code`. The search itself has to be initiated with a subsequent call to `ow.search()`.
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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, I/O 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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Writes 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, I/O index
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- `v` byte 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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## ow.write_bytes()
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Writes 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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