onewire — 1-Wire bus protocol

The onewire module implements the 1-Wire bus master protocol used by devices such as the DS18x20 temperature sensor. It uses a single machine.Pin configured as open-drain to communicate with one or more slave devices on the shared bus.

Example:

from machine import Pin
from onewire import OneWire

ow = OneWire(Pin(15))
devices = ow.scan()
for rom in devices:
    print(rom)

Classes

class onewire.OneWire(pin: machine.Pin)

Construct a 1-Wire bus master on the given machine.Pin. The pin is automatically configured as open-drain with a pull-up.

ROM command constants:

SEARCH_ROM: int

Search ROM command (0xF0). Used internally by scan() to discover devices on the bus.

MATCH_ROM: int

Match ROM command (0x55). Used internally by select_rom() to address a specific device by its 64-bit ROM code.

SKIP_ROM: int

Skip ROM command (0xCC). Addresses all devices on the bus simultaneously, skipping ROM matching.

Bus reset:

reset(required: bool = False) → bool

Issue a reset pulse on the bus. Returns True if at least one slave device responded with a presence pulse, otherwise False. If required is True and no device responds, raises OneWireError.

Bit/byte I/O:

readbit() → int

Read a single bit from the bus and return it as 0 or 1.

readbyte() → int

Read a single byte from the bus and return it as an integer (0–255).

readinto(buf: bytearray) → None

Read len(buf) bytes from the bus into the given pre-allocated buffer.

writebit(value: int) → None

Write a single bit (0 or 1) to the bus.

writebyte(value: int) → None

Write a single byte (0–255) to the bus.

write(buf: bytes | bytearray) → None

Write the bytes in buf to the bus.

Device addressing:

select_rom(rom: bytes | bytearray) → None

Issue a reset followed by a MATCH ROM command to address the device whose 64-bit ROM code is in rom (an 8-byte buffer).

scan() → list[bytearray]

Search the bus and return a list of 8-byte ROM codes (one bytearray per detected device). Returns an empty list if no devices are present.

Cyclic redundancy check:

crc8(data: bytes | bytearray) → int

Compute the Maxim/Dallas 8-bit CRC over data. The result is 0 when data already includes a valid trailing CRC byte, which can be used to validate received scratchpad contents.

Exceptions

exception onewire.OneWireError

Raised when a 1-Wire operation fails. Currently raised by OneWire.reset() when required is True and no slave responds to the reset pulse.