ModbusRTU.h with SoftwareSerial example not working

[Ashton]

I'm trying to use the ModbusRTU.h library with SoftSerial.h using this example
I'm working with a 32-Input Modbus module, simply trying to poll the inputs to read On states (0=off, 1=on) of a holding register in this example. I have tested this module with other example (function 03) reads found in the manufacturer's instructions using Arduino Nano with MAX485 module, and Modbus Poll, a Modbus Master app for slave testing -- all works perfect.

My code:

#include <ModbusRtu.h>
#include <SoftwareSerial.h>

// data array for modbus network sharing
uint16_t au16data[32];
uint8_t u8state;

SoftwareSerial mySerial(2, 3);//Create a SoftwareSerial object so that we can use software serial. Search "software serial" on Arduino.cc to find out more details.

/**
 *  Modbus object declaration
 *  u8id : node id = 0 for master, = 1..247 for slave
 *  port : serial port
 *  u8txenpin : 0 for RS-232 and USB-FTDI 
 *               or any pin number > 1 for RS-485
 */
Modbus master(0, mySerial); // this is master and RS-232 or USB-FTDI via software serial

/**
 * This is an structe which contains a query to an slave device
 */
modbus_t telegram;

unsigned long u32wait;

void setup() {
  Serial.begin(9600);
  mySerial.begin(9600);//use the hardware serial if you want to connect to your computer via usb cable, etc.
  master.start(); // start the ModBus object.
  master.setTimeOut( 2000 ); // if there is no answer in 2000 ms, roll over
  u32wait = millis() + 1000;
  u8state = 0; 
}

void loop() {
  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 = 128; // start address in slave
    telegram.u16CoilsNo = 32; // 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) 
    {
        Serial.print("STATE:");
        Serial.println(master.getState());  // 0
        Serial.print("ERROR:");
        Serial.println(master.getLastError());  // 0 Errors
        Serial.print("READ DATA:");
        Serial.println(au16data[0]);  // 0, never a 1 with input
        u32wait = millis() + 1000;
        u8state = 0;
    }
    break;
  }
}

Is this more of the same problems from smarmengol?

I have the below array value properly selected to print I believe.

Serial.println(au16data[0]);//Register 1 value

I suppose there is no way to see/read the query hex frame being sent to the I/O module without a serial analyzer app, when using a library.

[Ashton]

I found a solution to this issue, a really simple alternative to this that works perfectly.
here

Code found at bottom of this blog.