Understanding modbus library function for arduino

Projects General Guidance
1

I have a device with which I want to communicate and read it's data. It's data starts at 3000H. I am making use of Juan Bester modbus library for arduino. Regarding the circuit, everything is sorted out. But it's the library, that I have tough time to understand. Link

I was able to communicate successfully using RS485 converter, but with arduino no luck.

Here is the code to read register at address 3000H for a slave id 42. Let me know if I am wrong.

#include <SimpleModbusMaster_DUE.h>
long previousMillis = 0;
long interval = 1000;
//////////////////// Port information ///////////////////
#define baud 19200
#define timeout 1000
#define polling 200 // the scan rate
#define retry_count 10
#define TxEnablePin 2 

#define LED 13

// The total amount of available memory on the master to store data
#define TOTAL_NO_OF_REGISTERS 8

enum
{
  PACKET1,
  //PACKET2,
  //PACKET3,
  TOTAL_NO_OF_PACKETS // leave this last entry
};

Packet packets[TOTAL_NO_OF_PACKETS];

unsigned int regs[TOTAL_NO_OF_REGISTERS];
void setup()
{

  modbus_construct(&packets[PACKET1], 42, READ_HOLDING_REGISTERS, 0x3000, 8, 8);

  modbus_configure(&Serial, baud, timeout, polling, retry_count, TxEnablePin, packets, TOTAL_NO_OF_PACKETS, regs);

  //pinMode(LED, OUTPUT); 
}
void loop()
{
  modbus_update();
    regs[0] = analogRead(0); 
    analogWrite(LED, regs[0]>>2); 

}

According to the manual, the device adopts CRC-16 method. The above code is exactly same as the library example. I have just changed the parameters of baud rate and reading holding register for the device.

modbus_construct(&packets[PACKET1], 42, READ_HOLDING_REGISTERS, 0x3000, 8, 8);

Now, I am having no clue of how to process a slave response. How should I know! that a slave is responding. And if it is responding, then where in my code I should decode the response.

In the void loop() I tried to print regs[0]. But it gives value that is nowhere near to readings of my device.

Thanks in advance