Arduino to Arduino Modbus RTU in RS-485 - arduino

Question

I'm trying Arduino to Arduino (master-slave) communication using Modbus RTU protocol in RS-485. I am using an Arduino Mega 2560 for the project and using this library Modbus RTU. As of now, the master simply reads data slave and prints in the Serial monitor.
I tried the following code:
Slave
#include <ModbusRtu.h>
#define ID 3
Modbus slave(ID, 0, 0);
boolean led;
int8_t state = 0;
unsigned long tempus;
// data array for modbus network sharing
uint16_t au16data[9];
void setup() {
// define i/o
pinMode(2, INPUT);
pinMode(3, INPUT);
pinMode(4, INPUT);
pinMode(5, INPUT);
// start communication
slave.begin(19200);
tempus = millis() + 100;
digitalWrite(13, HIGH);
}
void loop() {
// poll messages
// blink led pin on each valid message
state = slave.poll( au16data, 9 );
if (state > 4) {
tempus = millis() + 50;
digitalWrite(13, HIGH);
}
if (millis() > tempus) digitalWrite(13, LOW );
// get digital inputs -> au16data[0]
bitWrite( au16data[0], 0, digitalRead( 2 ));
bitWrite( au16data[0], 1, digitalRead( 3 ));
bitWrite( au16data[0], 2, digitalRead( 4 ));
bitWrite( au16data[0], 3, digitalRead( 5 ));
// diagnose communication
au16data[6] = slave.getInCnt();
au16data[7] = slave.getOutCnt();
au16data[8] = slave.getErrCnt();
}
Master
#include <ModbusRtu.h>
// data array for modbus network sharing
uint16_t au16data[16];
uint8_t u8state;
/**
* Modbus object declaration
* u8id : node id = 0 for master, = 1..247 for slave
* u8serno : serial port (use 0 for Serial)
* u8txenpin : 0 for RS-232 and USB-FTDI
* or any pin number > 1 for RS-485
*/
Modbus master(0,1,1); // this is master and RS-485
/**
* This is an structe which contains a query to an slave device
*/
modbus_t telegram;
unsigned long u32wait;
void setup() {
master.begin(19200); // baud-rate at 19200
master.setTimeOut(2000); // if there is no answer in 2000 ms, roll over
u32wait = millis() + 1000;
u8state = 0;
Serial.begin(9600);
}
void loop() {
Serial.print(u8state);
switch(u8state) {
case 0:
if (millis() > u32wait) u8state++; // wait state
break;
case 1:
telegram.u8id = 1; // slave address
telegram.u8fct = 3; // function code (this one is registers read)
telegram.u16RegAdd = 1; // start address in slave
telegram.u16CoilsNo = 4; // number of elements (coils or registers) to read
telegram.au16reg = au16data; // pointer to a memory array in the Arduino
master.query(telegram); // send query (only once)
u8state++;
break;
case 2:
master.poll(); // check incoming messages
if (master.getState() == COM_IDLE) {
u8state = 0;
u32wait = millis() + 100;
}
break;
}
Serial.println(au16data[0])
}
The output in the serial monitor is not changed when the input at Pin 2 is high in slave.
20
00
Could someone please tell me the possible cause and solution? If I've missed out anything, over- or under-emphasized a specific point, let me know in the comments.