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I2C_MASTER/I2C_MASTER.ino

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+/*
+ * Echo Server Test
+ * Send one byte to the Echo Server and read it back.
+ * Do it for bytes from 0x01 to 0xDD
+ */
+#include <Wire.h>
+
+#define SLAVE_ADDRESS  0x0B
+byte car = 1; // car to be send to the Echo Server.
+
+void setup() {
+    Serial.begin(9600);
+  // We have a nodeMCU con I2C on pins D5 and D6.
+    Wire.begin();
+    delay(1000);
+  Serial.println("");
+    Serial.println(" Echo Server Tester");
+    Serial.println("---------------------");
+    Serial.println("###  Sent   Received");
+    delay(1000);    
+}
+
+/*
+ * Send one byte in each loop().
+ */
+void loop() {
+    byte status;
+
+    if(car > 0) {
+        do {
+            Wire.beginTransmission(SLAVE_ADDRESS);
+            int written = Wire.write(car);
+            status = Wire.endTransmission();
+
+            switch(status) {
+            case 0:
+                delay(1); // Comment this out and watch requestFrom() fails.
+                if(Wire.requestFrom(SLAVE_ADDRESS, 1) == 1) {
+                    byte r = Wire.read();
+                    printChar(car, r);
+                    car++;
+                } else {
+                    Serial.println("error in return");
+                    status = 4;
+                }
+
+                break;
+
+            case 1:
+                Serial.println("Data too long");
+                break;
+
+            case 2:
+                Serial.println("NACK on address");
+                break;
+
+            case 3:
+                Serial.println("NACK on data");
+                break;
+
+            case 4:
+                Serial.println("Some error");
+                break;
+            }
+        }
+
+        while(status != 0);
+    }
+}
+
+/*
+ * Utility: print in bytes sent and received 
+ */
+void printChar(byte s, byte r) {
+    Serial.print(s);
+    Serial.print(" ");
+    printBits(s);
+    Serial.print(' ');
+    printBits(r);
+
+    if(r != s) {
+    //  Mark invalid responses.
+        Serial.print(" *");
+    }
+
+    Serial.println();
+}
+
+/*
+ * Print a simple byte in binary
+ */
+void printBits(int car) {
+    byte bit = 0x80;
+
+    for(int i = 0; i < 8; i++) {
+        int digit = car & bit;
+        Serial.print(digit ? '1' : '0');
+        bit >>= 1;
+    }
+}