Modbus Master dengan software Modbus Slave

#include <ModbusRTU.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// OLED I2C (default address 0x3C untuk 128x64)
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_ADDR    0x3C
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

ModbusRTU mb;
int a = 0;
unsigned long skr = 0;
unsigned long lastDisplay = 0;   // timer untuk update OLED

bool koil1[3];
bool koil2[3];
bool koil3[3];
bool koil4[3];

void setup() {
  Serial.begin(9600, SERIAL_8N1);
  mb.begin(&Serial);
  mb.setBaudrate(9600);
  mb.master();

  pinMode(5, INPUT_PULLUP);
  pinMode(6, INPUT_PULLUP);
  pinMode(7, INPUT_PULLUP);
  pinMode(8, INPUT_PULLUP);

  // Inisialisasi OLED
  if (!display.begin(SSD1306_SWITCHCAPVCC, OLED_ADDR)) {
    // Jika gagal, diam saja (tidak mengganggu jalannya program)
    for (;;);
  }
  display.clearDisplay();
  display.setTextSize(2);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(0, 0);
  display.println("OLED Ready");
  display.display();
  delay(1000);
  display.clearDisplay();
}

void loop() {
  // ----- Scheduler Modbus (setiap 100ms) -----
  if (millis() - skr > 100) {
    skr = millis();
    a++;
    if (a > 11) a = 0;

    switch (a) {
      case 0:
        mb.readCoil(1, 0, koil1, 3);
        break;
      case 1:
        mb.readCoil(2, 0, koil2, 3);
        break;
      case 2:
        mb.readCoil(3, 0, koil3, 3);
        break;
      case 3:
        mb.readCoil(4, 0, koil4, 3);
        break;
      case 4:
        mb.writeCoil(1, 1, digitalRead(5));
        break;
      case 5:
        mb.writeCoil(2, 1, digitalRead(6));
        break;
      case 6:
        mb.writeCoil(3, 1, digitalRead(7));
        break;
      case 7:
        mb.writeCoil(4, 1, digitalRead(8));
        break;
      case 8:
        mb.writeCoil(1, 2, digitalRead(5));
        break;
      case 9:
        mb.writeCoil(2, 2, digitalRead(6));
        break;
      case 10:
        mb.writeCoil(3, 2, digitalRead(7));
        break;
      case 11:
        mb.writeCoil(4, 2, digitalRead(8));
        break;
    }
  }

  // Proses komunikasi Modbus
  mb.task();

  // ----- Update OLED setiap 300ms (agar tidak terlalu sering) -----
  if (millis() - lastDisplay > 300) {
    lastDisplay = millis();
    display.clearDisplay();
    display.setCursor(0, 0);

    // Baris 1 : koil1
    display.print("K1: ");
    for (int i = 0; i < 3; i++) {
      display.print(koil1[i] ? "1 " : "0 ");
    }
    display.println();

    // Baris 2 : koil2
    display.print("K2: ");
    for (int i = 0; i < 3; i++) {
      display.print(koil2[i] ? "1 " : "0 ");
    }
    display.println();

    // Baris 3 : koil3
    display.print("K3: ");
    for (int i = 0; i < 3; i++) {
      display.print(koil3[i] ? "1 " : "0 ");
    }
    display.println();

    // Baris 4 : koil4
    display.print("K4: ");
    for (int i = 0; i < 3; i++) {
      display.print(koil4[i] ? "1 " : "0 ");
    }
    display.println();

    display.display();
  }
}