Help with WeMos D1 Mini and NodeMCU in ModbusRTU RS485

Projects Networking, Protocols, and Devices
1

Hi, I have a project in making a Master-Slave Modbus Communication with RS485 using ArduinoIDE. The devices is a WeMos D1 Mini for Slave and a NodeMCU for Master. I use SimpleModbusMasterV2 and SimpleModbusSlaveV10.The code I'm using :

Master:

#include <SimpleModbusMaster.h>


//////////////////// Port information ///////////////////
#define baud 9600
#define timeout 1000
#define polling 200              // the scan rate
#define retry_count 10
#define TxEnablePin 2         //D4
#define LED 4                    //D2
#define TOTAL_NO_OF_REGISTERS 2

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

// Create an array of Packets to be configured
Packet packets[TOTAL_NO_OF_PACKETS];

// Masters register array
unsigned int regs[TOTAL_NO_OF_REGISTERS];

void setup()
{
  // Initialize each packet
  modbus_construct(&packets[PACKET1], 1, READ_HOLDING_REGISTERS, 0, 1, regs[0]);
  modbus_construct(&packets[PACKET2], 1, PRESET_MULTIPLE_REGISTERS, 1, 1,regs[1]);
  
  // Initialize the Modbus Finite State Machine
  modbus_configure(&Serial, baud, SERIAL_8N2, timeout, polling, retry_count, TxEnablePin, packets, TOTAL_NO_OF_PACKETS, regs);
  
  pinMode(LED, OUTPUT);
}

void loop()
{
  modbus_update();
  
  regs[1] = random(0,1024); // update data to be written to arduino slave
  analogWrite(LED, regs[0]);
  
  
}

and For Slave :

#include <SimpleModbusSlave.h>

#define TxEnablePin 2 //D4
#define LED 4 //D2


//////////////// registers of your slave ///////////////////
enum 
{     
  // just add or remove registers and your good to go...
  // The first register starts at address 0
  ADC_VAL,     
  PWM_VAL,        
  HOLDING_REGS_SIZE // leave this one
  // total number of registers for function 3 and 16 share the same register array
  // i.e. the same address space
};

unsigned int holdingRegs[HOLDING_REGS_SIZE]; // function 3 and 16 register array
////////////////////////////////////////////////////////////

void setup()
{
  /* parameters(HardwareSerial* SerialPort,
                long baudrate, 
 unsigned char byteFormat,
                unsigned char ID, 
                unsigned char transmit enable pin, 
                unsigned int holding registers size,
                unsigned int* holding register array)
  */
  
  /* Valid modbus byte formats are:
     SERIAL_8N2: 1 start bit, 8 data bits, 2 stop bits
     SERIAL_8E1: 1 start bit, 8 data bits, 1 Even parity bit, 1 stop bit
     SERIAL_8O1: 1 start bit, 8 data bits, 1 Odd parity bit, 1 stop bit
     
     You can obviously use SERIAL_8N1 but this does not adhere to the
     Modbus specifications. That said, I have tested the SERIAL_8N1 option 
     on various commercial masters and slaves that were suppose to adhere
     to this specification and was always able to communicate... Go figure.
     
     These byte formats are already defined in the Arduino global name space. 
  */
 
  modbus_configure(&Serial, 9600, SERIAL_8N2, 1, TxEnablePin, HOLDING_REGS_SIZE, holdingRegs);

  // modbus_update_comms(baud, byteFormat, id) is not needed but allows for easy update of the
  // port variables and slave id dynamically in any function.
  modbus_update_comms(9600, SERIAL_8N2, 1);
  
  pinMode(LED, OUTPUT);
}

void loop()
{
  
  modbus_update();
  
  holdingRegs[ADC_VAL] = 512;

  
}

The problem is I just can't get it working. The plan is to have the master read the slave register and PWM a LED. However, the LED just won't turn on. I tried to add-in

Serial.println(regs[0]);

to the Master in order to see what it's reading, but when i connect it into my computer, my mouse start randomly clicking and dragging.

I really hope someone can help me in this. Or if anyone have an actual working library, please tell me.

2

TOTAL_NO_OF_REGISTERS 1
?
you have 2 register

3

Juraj:
TOTAL_NO_OF_REGISTERS 1
?
you have 2 register

JuraJ, you're right. I completely miss that.

However, it's still don't work, i try to connect it without the RS485 (direct Tx-Rx between Master Slave) and it work, but when I try to use RS485 it won't read the register.

4

HollowLord:
However, it's still don't work, i try to connect it without the RS485 (direct Tx-Rx between Master Slave) and it work, but when I try to use RS485 it won't read the register.

then it is a wiring problem. terminators?

5

Juraj:
then it is a wiring problem. terminators?

I'm using a module for RS485 (it should have a 120Ohm Resistor installed). How do you see whether it have the terminator or not?

I rewired everything, i doubt it's the wiring. The module i'm using have the 120 Ohm terminator installed.

6

Project update:

I used these code to examine the communication between Master-RS485 <--> RS485-Slave

Master

void setup(){
Serial.begin(9600);
pinMode(2,OUTPUT); //DE-RE
}

void loop(){
digitalWrite(2,HIGH) //Transmit mode
Serial.write("Hello World");
delay(10000);

}

Slave

void setup(){
Serial.begin(9600);
pinMode(2,OUTPUT); //DE-RE
}

void loop(){
digitalWrite(2,LOW) //Receive Mode
Serial.write(Serial.read());
delay(100);

}

And there no problem with the RS-485 communication, both end able to transmit and receive normally. My guess is there a problem with the library, however i'm no expert in that. Please help!