Hello @felmue,

thank you very much for your quick support, it really helped me.

It didn't work in my "big" program, but I wrote a small test program, and it fully meets the requirements:

#include <M5StamPLC.h>       

void my_set_backlight(bool o) {
  PI4IOE5V6408_Class p;
  p.setDirection(7, true);  // false input, true output
  p.digitalWrite(7, !o);    // false on, true off
}

void printAndWait(String s) {
  M5StamPLC.Display.println(" " + s);
  delay(4000);
}

void setup() {
  Serial.begin(115200);
  M5StamPLC.begin(); 
  M5StamPLC.Display.setTextSize(3);
}

void loop() {
  M5StamPLC.Display.fillScreen(TFT_BLACK);
  M5StamPLC.Display.setCursor(0, 10);
  printAndWait("Test 1");
  printAndWait("Test 2");
  my_set_backlight(false);
  printAndWait("Test 3");
  my_set_backlight(true);
  printAndWait("Test 4");
}

You can see it not only in the dark screen, but also in the power consumption, which is reduced by about 20%.

I suspect that in my "big" program, someone is turning the lights back on (and working against me).

Best regards,
Uwe

The solution from Chat.M5Stack.com didn't work either:

#include <M5StamPLC.h>
#include <Wire.h>

#define PI4IOE5V6408_ADDR 0x43  // I2C-address
#define DIR_REG 0x06                 
#define OUTPUT_REG 0x02      

void setup() {
  M5StamPLC.begin();  // Initialisiert I2C-Bus (G15=SCL, G13=SDA)
  
  // P7 (LCD_BL) is output, Set Bit 7 of DIR_REG = 0
  Wire.beginTransmission(PI4IOE5V6408_ADDR);
  Wire.write(DIR_REG);
  Wire.write(0x7F);  // 0b01111111 (only P7=output)
  Wire.endTransmission();
}

void setBacklight(bool on) {
  Wire.beginTransmission(PI4IOE5V6408_ADDR);
  Wire.write(OUTPUT_REG);
  Wire.write(on ? 0xFF : 0x7F);  // P7=1 (on) or 0 (off)
  Wire.endTransmission();
}

Hello,
I would like to turn off the backlight of the M5StamPLC when there's nothing to see.
The set_backlight function from the M5 library doesn't seem to work. The reason
is probably that there is no "normal" LCD_BL pin:

// Display
#define STAMPLC_PIN_LCD_MOSI 8
#define STAMPLC_PIN_LCD_MISO 9
#define STAMPLC_PIN_LCD_SCLK 7
#define STAMPLC_PIN_LCD_DC 6
#define STAMPLC_PIN_LCD_CS 12
#define STAMPLC_PIN_LCD_RST 3
#define STAMPLC_PIN_LCD_BUSY -1
#define STAMPLC_PIN_LCD_BL -1

In the M5StamPLC, the PI4IOE5V6408 is responsible for the backlight, and pin 7 is responsible for it.

Unfortunately, my own routine doesn't work either:

void my_set_backlight(bool o) {
  PI4IOE5V6408_Class p;
  // false input, true output
  p.setDirection(7, true);
  // false off, true on ?
  p.digitalWrite(7, o);
}

Does anyone have an idea, or even better, a solution?

Hello,

my RS485-reader on a M5StamPLC worked fine with the standard Arduino Libraries on Serial1. If I use M5StamPLC-Library like #include <M5StamPLC.h> and if I use the M5StamPLC.begin(); then Serial1 didn‘t work anymore.

void setup() {
   M5StamPLC.begin(); <— Didn‘t work. Serial1.available never find an input
   Serial1.begin(38400, SERIAL_8N1, RX_PIN, TX_PIN);
}

void loop() {
   while (Serial1. available) {
       char incomingByte = Serial1.read();
       …
   }
}

I can‘t find the init-calls for RS485 in M5StamPLC and not in M5Unified.

Who can help?