Introduction

This post, it is showed how to test the RS-485 on M-Duino PLUS version.

The first thing that you need to know is that the  RS-485 PLUS version has Full and Half-Duplex communication. Controlling the dip switch, you must select if you want to work on Full or Half-Duplex. There is internally installed a Half duplex MAX485 and MAX485 transmitter. If you are working on Full-Duplex you will use the MAX485 Half-Duplex to receive data and MAX485 transmitter to send the data.

The pin mapping is shown below:

Requirements 

• Ethernet PLC:          M-Duino Family Products

• RS-485 Library Basics:    Industrial Shields RS-485 Basics

Configuration

To do the Full-Duplex test, you must connect the A, B (receivers) to the Y, X(transmitters). For Half-Duplex, you must connect with another device with RS-485 and select if you want to transmit or receive data with a comment or uncomment “#define” command:

In Half-Duplex sketch:

• For transmitting:

#define TEST_RS485_TX
//#define TEST_RS485_RX

• For receiving:

//#define TEST_RS485_TX
#define TEST_RS485_RX

Software

Next it is showed the test sketch for Half-Duplex: 

(by default it is in transmitter mode)

#define TEST_RS485_TX
//#define TEST_RS485_RX
 
int _rs485DE = 46;
int _rs485RE = 11;

///////////////////////////////////////////////////////////////////////////////
void setup() {
  Serial.begin(9600L);
  Serial.println("M-Duino PLUS RS-485 test started");
  
  Serial3.begin(9600L);
  pinMode(_rs485RE, OUTPUT);
  digitalWrite(_rs485RE, LOW);
  pinMode(_rs485DE, OUTPUT);
  digitalWrite(_rs485DE, LOW);
}
//////////////////////////////////////////////////////////////////////////////
void loop() {

#if defined TEST_RS485_TX
  digitalWrite(_rs485RE, HIGH);
  digitalWrite(_rs485DE, HIGH);
  Serial3.write(0x12);
  Serial3.flush();
  digitalWrite(_rs485DE, LOW);
  digitalWrite(_rs485RE, LOW);
  delay(1000);
#endif // TEST_RS485_TX

#if defined TEST_RS485_RX
  if (Serial3.available()) {
    if (Serial3.read() == 0x12) {
      Serial.println("RX");
    }
   }
#endif // TEST_RS485_RX
}

Next it is showed the test sketch for Full-Duplex:

int _rs485DE = 46;
int _rs485RE = 11;

///////////////////////////////////////////////////////////////////////////////
void setup() {
  Serial.begin(9600L);
  Serial.println("M-Duino PLUS RS-485 test started");
  
  Serial3.begin(9600L);
  pinMode(_rs485RE, OUTPUT);
  digitalWrite(_rs485RE, LOW);
  pinMode(_rs485DE, OUTPUT);
  digitalWrite(_rs485DE, LOW);
}
//////////////////////////////////////////////////////////////////////////////
void loop() {
  digitalWrite(_rs485RE, HIGH);
  digitalWrite(_rs485DE, HIGH);
  Serial3.write(0x12);
  Serial3.flush();
  digitalWrite(_rs485DE, LOW);
  digitalWrite(_rs485RE, LOW);
  delay(1000);

  if (Serial3.available()) {
    if (Serial3.read() == 0x12) {
      Serial.println("RX");
    }
   }
}

See also

M-Duino Family RS-485 Help Page