Wire

Wire#

A single data wire plus ground. The slave parasitically draws power from the data line when it is idle high, so two physical conductors carry power, ground, and signal between a master and many slaves. iButtons, Dallas DS18B20 temperature sensors, some door-access tokens; each slave has a unique 64-bit ROM ID that the master uses to address it.

Wires#

Signal

Direction

Purpose

DQ

Bidirectional

Data and parasitic power; open-drain with a pull-up (typically 4.7 kΩ).

GND

Reference

Ground.

Vdd (optional)

In

Direct power; lets slaves skip parasitic mode.

Wire format#

The master initiates every transaction with a reset pulse. All slaves respond with a presence pulse, then the master issues a ROM command followed by a function command.

  • Reset. Master pulls DQ low for ≥ 480 µs, then releases.

  • Presence. Slaves pull DQ low for 60–240 µs.

  • Write 1. Master pulls low for 1–15 µs, releases for the rest of a 60 µs slot.

  • Write 0. Master pulls low for 60–120 µs.

  • Read slot. Master pulls low for 1 µs, releases, then samples DQ within 15 µs of the leading edge.

Speeds are 16.3 kbps standard and 142 kbps in overdrive mode. ROM commands address one or all slaves; function commands depend on the device family.

Pads#

Label

Meaning

DQ, DATA, IO

Single-wire data line.

GND

Ground.

VDD, VCC

Optional direct supply.

The 64-bit ROM ID is the operator’s interest. Family code (8 bits) + serial number (48 bits) + CRC (8 bits); some access tokens are cloned by copying the ROM ID into a writable iButton blank.

Tools#

Tool

Effect

DS2480B, DS2482

1-Wire bridge ICs; USB-to-1-Wire dongles use them internally.

w1-gpio (Linux kernel)

Bit-bang 1-Wire from a Raspberry Pi GPIO; surfaces slaves under /sys/bus/w1/devices/.

Flipper Zero, Proxmark3

Read and emulate iButton-style 1-Wire tokens.

Logic analyzer (Saleae, PulseView)

Decode 1-Wire timing.

References#

  • Maxim AN937 Book of iButton Standards.

  • Linux kernel Documentation/w1/ for the in-tree drivers.

  • I2C for the addressed two-wire alternative.

  • Sigrok 1-Wire decoder.

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