This repository contains I2C address scanners for the ATmega328p AVR and the GigaDevice GD32VF103CBT6 RISC-V MCU platforms.

How to use it: Hookup your I2C devices to a - say - Arduino Pro Mini 3.3 V (8 MHz) or a Longan Nano MCU board, upload a program from this repository and connect to the UART to watch the scanning progress.

Use case: For checking if the MCU's I2C unit, connected devices and I2C connections and the bus works in principle at certain speeds and pull-up resistor values. Or for simply verifying the address of a certain I2C device.

See also my I2C blog post for an extended discussion.

Build Instructions

The simplest way to build and upload a program is to use PlatformIO.

For the Atmega328p version:

cd atmega328p
pio project init --board pro8MHzatmega328 --ide vim
make upload

GD32VG103 (Longan Nano) version:

cd gd32vf103
pio project init --board gd32vf103c_longan_nano --ide vim
make upload

Example Output

$ picocom --baud 38400 /dev/ttyUSB0
Scanning I2C bus at 100 kHz ...
Found device on address: 0x60 (96)
Found device on address: 0x68 (104)
Scanning I2C bus at 400 kHz ...
Found device on address: 0x60 (96)
Found device on address: 0x68 (104)
done

[.. scan cycle repeats after 30 s or so ..]

ATmega328p Notes

This ATmega328p I2C scanner is written in C and only uses avr-libc headers, i.e. it doesn't use any Arduino libraries/APIs.

Thus, it's also an illustration of direct interfacing with AVR's I2C (a.k.a. 2-wire, Two Wire Interface (TWI)) unit. See also the ATmega328p datasheet (Section 22) for details. Arguably, interfacing with the MCU directly is just a little bit more verbose than using the object oriented abstraction the Arduino framework provides (cf. Wire.h). Perhaps the ATmega328p I2C register interface already is relatively high level, e.g. one doesn't need to poll for the I2C bus being free for sending a START, the MCU implements polling and START transmission as one atomic operation and one just has to poll (or wait) for START being completed.

The AVR version targets devices with 8 MHz CPU frequency, for other configurations one has to adjust the I2C clock frequency setup functions.

GD32VF103 Notes

The GD32VF103 version is also written in C and uses the Nuclei SDK, which (unlike the avr-libc) already provides an API for I2C. Thus, this version is a bit shorter. However, the setup code is more complex than the AVR MCU one. The GD32VF103 User Manual describes the I2C unit on a register and procedural level, such that one has to map that description to the Nuclei API. (reading the source code helps) However, the manual arguably is less accessible and complete than - say - the ATmega 328p one, certainly it leaves some setup and usage aspects open.

Thus, one has to experiment a bit when creating an I2C program from scratch.

Related Work

• Wolfgang Ewald's I2C scanner that uses the Arduino Wire.h API (2020)
• Nick Gammon's I2C scanner that also uses Arduino's Wire.h API (2011)
• Andreas Müller's I2C C++ class for the Longan Nano and an example for interfacing with an LCD