How to use ModbusRTUSlave library by Bullinar without usb

Projects Programming
1

Hi I am trying to use the ModbusRTUSlave library by CM Bullinar . I am using a Nano and USB-RS485 converter by EasySYNC which I have used extensively. Is it possible to define pins 10 and 11 as RX and TX so that the usb port remains usable with this library? I borrowed the code for that from the master version of the library. my code loads but polling from a master leads to time out at the read holding register function. (thats a Labview modbus client which I use routinely and works with the modbus running through the usb connection). Has anyone done this successfully or know a library that is easy to use this way?


```cpp
#include <SoftwareSerial.h>
#include <ModbusRTUSlave.h> // ModbusRTUSlave by CM Bullinar

ModbusRTUSlave modbus_slave(Serial);
const uint8_t slaveID = 1;
const uint32_t baud = 9600;
// Define software serial pins for RX and TX
#define RX_PIN 10
#define TX_PIN 11

// Create a software serial port
SoftwareSerial mySerial(RX_PIN, TX_PIN);

uint16_t holdingRegisters[20] = {0};

int sensor;
void setup() {
  // put your setup code here, to run once:
modbus_slave.configureHoldingRegisters(holdingRegisters, 21);
modbus_slave.begin(slaveID, baud, SERIAL_8N1);
}

void loop() {
  // put your main code here, to run repeatedly:
sensor = analogRead(A0);
holdingRegisters[0] = sensor;
modbus_slave.poll();

}
2

Should'n you put your software serial there?

3

I am guessing you mean the (serial) bit is specifying the arduino usb and I should change it to something else?

4

Yes.
Should be mySerial as you defined connection for modbus

5

I did that but still not working, maybe i put it in the wrong place?

#include <SoftwareSerial.h>
#include <ModbusRTUSlave.h> // ModbusRTUSlave by CM Bullinar


const uint8_t slaveID = 1;
const uint32_t baud = 9600;
// Define software serial pins for RX and TX
#define RX_PIN 10
#define TX_PIN 11

// Create a software serial port
SoftwareSerial mySerial(RX_PIN, TX_PIN);
ModbusRTUSlave modbus_slave(mySerial);
uint16_t holdingRegisters[20] = {0};

int sensor;
void setup() {
  // put your setup code here, to run once:
modbus_slave.configureHoldingRegisters(holdingRegisters, 21);
modbus_slave.begin(slaveID, baud, SERIAL_8N1);
}

void loop() {
  // put your main code here, to run repeatedly:
sensor = analogRead(A0);
holdingRegisters[0] = sensor;
modbus_slave.poll();

}
6

Try like this at baudrate 4800

#include <SoftwareSerial.h>
#include <ModbusRTUSlave.h> // ModbusRTUSlave by CM Bullinar


const uint8_t slaveID = 1;
const uint32_t baud = 4800;
// Define software serial pins for RX and TX
#define RX_PIN 10
#define TX_PIN 11

// Create a software serial port
SoftwareSerial mySerial(RX_PIN, TX_PIN);
ModbusRTUSlave modbus_slave(mySerial);
uint16_t holdingRegisters[2];

int sensor;
void setup() {
  // put your setup code here, to run once:
modbus_slave.configureHoldingRegisters(holdingRegisters, 2);
modbus_slave.begin(slaveID, baud, SERIAL_8N1);
}

void loop() {
  // put your main code here, to run repeatedly:

holdingRegisters[0] = 333;
holdingRegisters[1] = 777;
modbus_slave.poll();
delay(10);
7

Kmin, Thanks for your help I have given up as it is easier just to use the USB.

8

Of course :+1: