Arduino for STM32

Hi,

I can't make the simple "Hello, World" show on 16x2 LCD monitor. First, what seems to be OK:

The HD44780 + PCF8574, factory soldered. It works normally with ESP32 processor dangling on the USB cable plugged into the same laptop's USB port. The internal PCF8574 pull-up resistors measure at 4.5k, which is probably slightly better than just OK.

Arduino IDE 2 settings:

Board: "Generic STM32F1 series"
Port: "/dev/tty/ACM0" (grayed out)
Debug symbols and core logs: "None"
Optimize: "Smallest (-Os default)"
Board part number: "BluePill F103C8"
C Runtime Library: "Newlib Nano (default)"
Upload method: "HID Bootloader 2.2"
USB support (if available): "CDC (generic 'Serial' supersede U(S)ART)"
U(S)ART support: "Enabled (generic 'Serial')"
USB speed (if available): "Low/Full Speed"

Breadboard connections:

STM32F103C8T6 PCF8574

GND --- GND
5V --- VCC
B6 --- SCL
B7 --- SDA

The only sketch to show any consistency is the I2CScanner:

Scanning...
I2C device found at address 0x27 !
done

Which is exactly what I'd expect.

All the libraries like LiquidCrystalI2C just won't work, so I tried Wire-only solution, just to look at error messages.

#include <Wire.h>

void WirebeginTransmission() {
Wire.beginTransmission(0x27);
}

const char* DecodeEndTransmission(unsigned errorCode) {
switch (errorCode) {
case 1: return "data too long to fit in transmit buffer";
case 2: return "received NACK on transmit of address";
case 3: return "received NACK on transmit of data";
case 4: return "other error";
case 5: return "timeout";
default: return (errorCode ? "UNKNOWN" : "ZERO");
}
}

void WireendTransmission(char* msg) {
unsigned code = Wire.endTransmission();
if (code > 0 && msg != NULL) {
Serial.printf("endTransmission: \"%s\" %s\n", msg, DecodeEndTransmission(code));
}
}

void setup() {
Serial.begin(9600);
while(!Serial);
Wire.begin();
Wire.setClock(400000);
WirebeginTransmission();
Wire.write(0x01); // Clear display

WireendTransmission("setup");
}

unsigned count = 0;

void loop() {
Serial.printf(">>%d<<\n", count++);
WirebeginTransmission();
Wire.write(0x80); // Set cursor to the first line
Wire.write("Hello, World!");
WireendTransmission("loop");
delay(1000);
}

I can only see endTransmission: "loop" other error; if I comment out all the Wire.write() inside loop(), I can see endTransmission: "loop" received NACK on transmit of address. Besides, the display doesn't get reliably cleared in spite of the alleged success.

It looks like power supply problem; I even plugged the programmed assembly into USB power supply 1500mA, but is won't show any difference. I tried different Wire.setClock() values, including the default. No difference.

What else can I check?

Add pullup resistors on each i2c lines.

As a matter of fact, I did. No difference. Used my multi-meter later to discover that built-in pull-up resistors measure at 4.5k.

be careful HD44780 works at different voltage from 3.3v
and that normally it isn't i2c

The voltage on 5V/VCC checked: 5V indeed.

One day it just started to work. Probably, unreliable contact with SCL or SDA line at the backpack. At least, all the other suspects, including USB cables, turned out to be innocent. Among other things, changed three LCD displays, It's possible that a modicum of friction made the metal inside the holes cleaner and the contact better