A LCD via the I2C bus on STM32 boards stopped working in Arduino mode.

[Koepel]

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In the Discord channel was mentioned that the I2C bus does not work for the STM32 board in Arduino mode.

There is more than one problem:

1. The local files for the I2C LCD display with "Wire2" do no longer work.
2. There seems to be no longer a compatible I2C LCD library .

Large STM32 Nucleo64 C031C6 board: Example for old situation: https://wokwi.com/projects/365421666018061313 When I do a Serial.println(SDA) and Serial.println(SCL) then the default pins are: SDA = 14 and SCL = 15.

Small STM32 Nucleo32 L031K6: Example for old situation: https://wokwi.com/projects/367245102561225729 With Serial.println(SDA) and Serial.println(SCL), then the default pins are: SDA = 4 and SCL = 5.

Tests: A sketch with a I2C Scanner on the default SDA and SCL pins work. A display and a RTC module are detected. However, the "LiquidCrystal I2C" library does not work for the display, and even the "hd44780" library does not work. I can not find any STM32 project with a working I2C LCD display. I don't know if a OLED display works. The Adafruit GFX library with the Adafruit SSD1306 does not compile.

[Koepel]

Test with a DS1307 to pins 4,5 (small board) or 14,15 (large board):

#include <Wire.h>

void setup() 
{
  Wire.begin();

  Wire.beginTransmission(0x68);
  Wire.endTransmission();

  delayMicroseconds(50);

  Wire.beginTransmission(0x68);
  Wire.write(0);
  Wire.endTransmission();
}

void loop() {}

Result for both boards:

The SCL is stuck to low when a databyte should be transmitted. That explains that only a I2C Scanner works.

[urish]

Issue reproduced - seems to be a regression introduced by #744