first commit

I2C_SLAVE/I2C_SLAVE.ino

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+/*
+ * I2C Echo Server
+ * Receive one byte from Master, echo the same byte to Master.
+ */
+#define MY_ADDRESS  0x0B
+
+#include <Wire.h>
+
+volatile byte received;
+volatile int count = 0;
+
+void setup() {
+  Serial.begin(9600);
+
+  Wire.begin(MY_ADDRESS);
+  Serial.println("--- Echo Server ---");
+
+  Wire.onReceive(receiveCommand);
+  Wire.onRequest(sendAnswer);
+}
+
+void loop() {
+  static int lastCount = 0;
+
+  if (count != lastCount) {
+    Serial.print(lastCount + 1); Serial.print(" ");
+    printChar(received);
+    lastCount++;
+  }
+}
+
+/*  
+ * Receive a byte from Master  
+ */
+void receiveCommand(int howMany) {
+  received = Wire.read();
+  count++;
+}
+
+/* 
+ * Send a byte to Master 
+ */
+void sendAnswer() {
+  Wire.write(received);
+}
+
+/*
+ * Utility print byte received/sent
+ */
+void printChar(byte car) {
+  Serial.print("Char ");
+  byte bit = 0x80;
+  for (int i = 0; i < 8; i++) {
+    byte digit = car & bit;
+    Serial.print(digit ? '1' : '0');
+    bit >>= 1;
+  }
+  Serial.println();
+}