UART, Modbus and custom commands

Projects General Guidance
3

Thank you. Reading through both the thread and the code, that seems to be a method to validate the checksum. I have the checksum (it is non-standard or, at least, non-common using Modulo 256). What I need to do is send the hex to the controller and receive the response.

Its also quite possible that I'm missing the key information in the links you posted.

What I think I am looking for is more like this thread but with the ability to send the hex string rather than poll a register.

It seems that as I am using an Uno, I also need to implement SoftwareSerial for the Uno>RS485.

Currently, I have this code that I'm looking to improve although I haven't yet figured out the SoftwareSerial changes that I need to make.

#include <ModbusMaster.h>
#include <SoftwareSerial.h>

#define MAX485_DE     3
#define MAX485_RE_NEG 2

ModbusMaster node;

void preTransmission()
{
  digitalWrite(MAX485_RE_NEG, 1);
  digitalWrite(MAX485_DE, 1);
}

void postTransmission()
{
  digitalWrite(MAX485_RE_NEG, 0);
  digitalWrite(MAX485_DE, 0);
}

void setup()
{
  // put your setup code here, to run once:
  pinMode(MAX485_RE_NEG, OUTPUT);
  pinMode(MAX485_DE, OUTPUT);
  // Init in receive mode
  digitalWrite(MAX485_RE_NEG, 0);
  digitalWrite(MAX485_DE, 0);

  // Modbus communication runs at 115200 baud
  Serial.begin(9600);

  //Modbus slave ID 1
  node.begin(1, Serial);
  // Callbacks allow us to configure the RS485 transceiver correctly
  node.preTransmission(preTransmission);
  node.postTransmission(postTransmission);
}

void loop()
{
  byte buf[] = {0x01, 0xA3, 0x01, 0x00, 0x00, 0x00, 0x00, 0xA5};
  Serial.write(buf, 8);
  Serial.write('\n');
  int hexIn = Serial.read();
  delay(30000);
}