#include <Wire.h>

#define SLAVE_ADDR 8
#define LED_PIN 13

void setup() {
  pinMode(LED_PIN, OUTPUT);
  Wire.begin(SLAVE_ADDR);         // 初始化 I2C 从机
  Wire.onReceive(receiveEvent);   // 注册接收函数
  Serial.begin(9600);
  Serial.println("Slave ready.");
}

void loop() {
  // 主循环无需操作，所有由中断处理
}

void receiveEvent(int bytes) {
  while (Wire.available()) {
    char c = Wire.read();
    Serial.print("Received: ");
    Serial.println(c);
    if (c == 'A') {
      digitalWrite(LED_PIN, HIGH);
    } else if (c == 'B') {
      digitalWrite(LED_PIN, LOW);
    }
  }
}