nodemcu-firmware/docs/modules/ow.md

1-Wire Module

Since	Origin / Contributor	Maintainer	Source
2014-12-22	Zeroday	Zeroday	ow.c

This module provides functions to work with the 1-Wire device communications bus system.

ow.check_crc16()

Computes the 1-Wire CRC16 and compare it against the received CRC.

Syntax

ow.check_crc16(buf, inverted_crc0, inverted_crc1[, crc])

Parameters

• buf string value, data to be calculated check sum in string
• inverted_crc0 LSB of received CRC
• inverted_crc1 MSB of received CRC
• crc CRC starting value (optional)

Returns

true if the CRC matches, false otherwise

ow.crc16()

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:

1. The CRC is transmitted bitwise inverted.
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.

Syntax

ow.crc16(buf[, crc])

Parameters

• buf string value, data to be calculated check sum in string
• crc CRC starting value (optional)

Returns

the CRC16 as defined by Dallas Semiconductor

ow.crc8()

Computes a Dallas Semiconductor 8 bit CRC, these are used in the ROM and scratchpad registers.

Syntax

ow.crc8(buf)

Parameters

buf string value, data to be calculated check sum in string

Returns

CRC result as byte

ow.depower()

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.

Syntax

ow.depower(pin)

Parameters

pin 1~12, I/O index

Returns

nil

####See also

• ow.write()
• ow.write_bytes()

ow.read()

Reads a byte.

####Syntax ow.read(pin)

Parameters

pin 1~12, I/O index

Returns

byte read from slave device

ow.read_bytes()

Reads multi bytes.

Syntax

ow.read_bytes(pin, size)

Parameters

• pin 1~12, I/O index
• size number of bytes to be read from slave device (up to 256)

Returns

string bytes read from slave device

ow.reset()

Performs a 1-Wire reset cycle.

Syntax

ow.reset(pin)

Parameters

pin 1~12, I/O index

Returns

• 1 if a device responds with a presence pulse
• 0 if there is no device or the bus is shorted or otherwise held low for more than 250 µS

ow.reset_search()

Clears the search state so that it will start from the beginning again.

Syntax

ow.reset_search(pin)

Parameters

pin 1~12, I/O index

Returns

nil

ow.search()

Looks for the next device.

Syntax

ow.search(pin)

Parameters

pin 1~12, I/O index

Returns

rom_code string with length of 8 upon success. It contains the rom code of slave device. Returns nil if search was unsuccessful.

See also

ow.target_search()

ow.select()

Issues a 1-Wire rom select command. Make sure you do the ow.reset(pin) first.

Syntax

ow.select(pin, rom)

Parameters

• pin 1~12, I/O index
• rom string value, len 8, rom code of the slave device

Returns

nil

Example

-- 18b20 Example
pin = 9
ow.setup(pin)
count = 0
repeat
  count = count + 1
  addr = ow.reset_search(pin)
  addr = ow.search(pin)
  tmr.wdclr()
until (addr ~= nil) or (count > 100)
if addr == nil then
  print("No more addresses.")
else
  print(addr:byte(1,8))
  crc = ow.crc8(string.sub(addr,1,7))
  if crc == addr:byte(8) then
    if (addr:byte(1) == 0x10) or (addr:byte(1) == 0x28) then
      print("Device is a DS18S20 family device.")
        repeat
          ow.reset(pin)
          ow.select(pin, addr)
          ow.write(pin, 0x44, 1)
          tmr.delay(1000000)
          present = ow.reset(pin)
          ow.select(pin, addr)
          ow.write(pin,0xBE,1)
          print("P="..present)
          data = nil
          data = string.char(ow.read(pin))
          for i = 1, 8 do
            data = data .. string.char(ow.read(pin))
          end
          print(data:byte(1,9))
          crc = ow.crc8(string.sub(data,1,8))
          print("CRC="..crc)
          if crc == data:byte(9) then
             t = (data:byte(1) + data:byte(2) * 256) * 625
             t1 = t / 10000
             t2 = t % 10000
             print("Temperature="..t1.."."..t2.."Centigrade")
          end
          tmr.wdclr()
        until false
    else
      print("Device family is not recognized.")
    end
  else
    print("CRC is not valid!")
  end
end

####See also ow.reset()

ow.setup()

Sets a pin in onewire mode.

Syntax

ow.setup(pin)

Parameters

pin 1~12, I/O index

Returns

nil

ow.skip()

Issues a 1-Wire rom skip command, to address all on bus.

Syntax

ow.skip(pin)

Parameters

pin 1~12, I/O index

Returns

nil

ow.target_search()

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().

Syntax

ow.target_search(pin, family_code)

Parameters

• pin 1~12, I/O index
• family_code byte for family code

Returns

nil

####See also ow.search()

ow.write()

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.

Syntax

ow.write(pin, v, power)

Parameters

• pin 1~12, I/O index
• v byte to be written to slave device
• power 1 for wire being held high for parasitically powered devices

Returns

nil

####See also ow.depower()

ow.write_bytes()

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.

Syntax

ow.write_bytes(pin, buf, power)

Parameters

• pin 1~12, IO index
• buf string to be written to slave device
• power 1 for wire being held high for parasitically powered devices

Returns

nil

####See also ow.depower()