Opta RS485 - I can`t read the response from PLC

[florin_bendrea]

Hello,
I am using Arduino Opta and Delta PLC DVP14SS2. With Modbus Poll I can send command to set coil successfully On or Off. After each command I get a response from PLC. The problem is with Opta. I can send command to set coil successfully On or Off but I can`t read the response. RS485.available() is [-1].

#include <Arduino.h>
#define DEBUG true  //set to true for debug output, false for no debug output
#define DEBUG_SERIAL if(DEBUG)Serial

#include <ArduinoRS485.h>
#include "CRC16.h"

void send_request_on_hex();
void send_request_off_hex();
void send_value_one();
void send_value_two();

CRC16 crc(CRC16_MODBUS_POLYNOME,
          CRC16_MODBUS_INITIAL,
          CRC16_MODBUS_XOR_OUT,
          CRC16_MODBUS_REV_IN,
          CRC16_MODBUS_REV_OUT);

int crc_low;
int crc_high;

constexpr auto baudrate{ 9600 };

// Calculate preDelay and postDelay in microseconds for stable RS-485 transmission
constexpr auto bitduration{ 1.f / baudrate };
constexpr auto wordlen{ 9.6f };  // OR 10.0f depending on the channel configuration
constexpr auto preDelayBR{ bitduration * wordlen * 3.5f * 1e6 };
constexpr auto postDelayBR{ bitduration * wordlen * 3.5f * 1e6 };


const int Req_on[] = {2, 5, 8, 0, 255, 0, 0x8E, 0x69};
const int Req_off[] = {2, 5, 8, 0, 0, 0, 0xCF, 0x99};

void setup() {
  delay(10000);
  DEBUG_SERIAL.begin(baudrate);
  RS485.begin(baudrate, SERIAL_8E1);
  RS485.setDelays(preDelayBR, postDelayBR);

}

void loop() {
  send_request_on_hex();
  delay(2000);
  send_value_one();
  delay(2000);
  send_request_off_hex();
  delay(2000);
  send_value_two();
  delay(2000);
}
void send_request_on_hex()
{
  byte i;
  DEBUG_SERIAL.println();
  DEBUG_SERIAL.println("Sending ON command");
  DEBUG_SERIAL.println();
  delay(1500);
  RS485.beginTransmission();
  for (i = 0; i < 8; i++)
  {
    DEBUG_SERIAL.print("- Sending: ");
    DEBUG_SERIAL.println(Req_on[i]);
    RS485.write(Req_on[i]);
  }
  RS485.endTransmission();
  
  RS485.receive();
  if (RS485.available() > 0)
  {
    DEBUG_SERIAL.println("Receiving...");
    DEBUG_SERIAL.println(RS485.read(), HEX);
    DEBUG_SERIAL.println(RS485.read(), HEX);
    DEBUG_SERIAL.println(RS485.read(), HEX);
    DEBUG_SERIAL.println(RS485.read(), HEX);
    DEBUG_SERIAL.println(RS485.read(), HEX);
    DEBUG_SERIAL.println(RS485.read(), HEX);
    DEBUG_SERIAL.println(RS485.read(), HEX);
    DEBUG_SERIAL.println(RS485.read(), HEX);

  }
  else{
    DEBUG_SERIAL.println("No data");
  }

  RS485.noReceive();
  
}