/* ********************************************************************************
 * Arduino_RcvFm_NXT.pde
 * Author     : CH, Chen (Taiwan)
 * Date       : 2011.5.21
 * Description: Arduino communicating with NXT via RS485
 *              Arduino receiving message sending from NXT
 * DFRobot I/O Expansion Shield for Arduino (DFR0088)
 * 1. RO(Data Output)     - Arduino D0(RX)
 * 2. RE(Receiver Enable) - Arduino D2 
 * 3. DE(Output Enable)   - Arduino D2 - HIGH/LOW - Transmit/Receive enable
 * 4. DI(Data Input)      - Arduino D1(TX)
 * 5. GND                 - NXT cable Pin 2/3 (GND)   (Black/Red)
 * 6. A                   - NXT cable Pin 5   (DIGI0) (Yellow)
 * 7. B                   - NXT cable Pin 6   (DIGI1) (Blue)
 * 8. VCC                 - Arduino +5V
 * ******************************************************************************** */
const int DE_RE_PIN = 2;         // The DFR0088 RS485 DE and RE pins are connected to Arduino D2, Set High/Low to enable Transmit/Receive data
const int MSG_LENGTH_LIMIT = 16;  
char rcvByte;
int byteIndex=0;
char rcvMessage [MSG_LENGTH_LIMIT];

void printMessage()
{
     Serial.print(byteIndex+1);
     Serial.println(" bytes received");
     for (int xi=0; xi <= byteIndex; xi++)
     {
         if (xi < byteIndex) Serial.print(rcvMessage[xi]);
         else                Serial.println(rcvMessage[xi]);
         rcvMessage[xi] = ' ';
     }
}

void setup()
{
    pinMode(DE_RE_PIN, OUTPUT);    
    Serial.begin(9600); 
}

void loop()
{
    digitalWrite(DE_RE_PIN, LOW);  // Enable data receive
    if (Serial.available() > 0)
    {
       rcvByte = Serial.read();       
       if ((rcvByte == '@') || (byteIndex == MSG_LENGTH_LIMIT)) // End of message receiving
       {          
          printMessage();
          byteIndex = 0;
          Serial.flush();
       }
       else
       {
          if ((rcvByte >= ' ') && (rcvByte <= 'z'))
          {
            rcvMessage[byteIndex] = rcvByte;
            byteIndex++;
          }
       }
    }     
}