Hi Guys

I'm quite afaid to enter this forum having no experience with programming at all so don't shoot yet 😎. All I want to do is read temperatures from a PT100 transmitter which say it used Modbus protocol (and it does, verified by someone else who has used it). The data sheet says:

Read Temp value, send command (example) 64 03 00 01 00 01 DC 3F (Device ID, function code, Register high bit, reg low bit, read number high bit, read number low bit, CRC_H, CRC_L).

Respnse will be: 64 03 02 01 0C 5F D9 (Device ID, function code, data byte numbers, Temp data high bit, Temp data low bit, CRC_H, CRC_L)

I wired the transmitter to A+ B-

After reading multitudes of examples from different libraries to try to understand a tiny bit, or byte, I used the code below.

There was no communication with the transmitter. It has a light that flashes and there was no light, and of course no data came through. I don't know what I don't know, so I'm looking for the error I have made if anyone can help I'd be most grateful.

#include ModbusRTUMaster

#if defined HAVE_RS485_HARD

#include

ModbusRTUMaster master(RS485); 

#elif defined HAVE_RS232_HARD

#include

ModbusRTUMaster master(RS232); 

#else

ModbusRTUMaster master(Serial1);

#endif

#define REGISTERS_TO_READ 2

const uint32_t baudrate = 9600;

uint32_t SlaveID = 0x64;

const uint16_t Address = 40002;

uint32_t lastSentTime = 0UL;

void setup() {

​Serial.begin(9600); // Start the serial port

​#if defined HAVE_RS485_HARD

​ ​RS485.begin(baudrate, HALFDUPLEX, SERIAL_8N1);

​#elif defined HAVE_RS232_HARD

​ ​RS232.begin(baudrate, SERIAL_8N1);

​#else

​ ​Serial1.begin(baudrate, SERIAL_8N1);

​#endif 

​master.begin(baudrate);

​Serial.println();

​Serial.println("Checking start....");

}

void loop() {

​Serial.println();

​Serial.println("Checking Loop....");

​ ​// Send a request every 1000ms

​if (millis() - lastSentTime > 925) {

​// Read REGISTERS_TO_READ holding registers, starting at address 0.

​// IMPORTANT: all read and write functions start a Modbus transmission, but they are not

​// blocking, so you can continue the program while the Modbus functions work. To check for

​// available responses, call master.available() function often.

​if (!master.readHoldingRegisters(SlaveID, 0, REGISTERS_TO_READ)) {

​// Failure treatment

}

​Serial.print("Last time sent = ");

​Serial.print(lastSentTime);

​Serial.println();

​lastSentTime = millis();

​// Check available responses often

​if (master.isWaitingResponse()) {

​ ​ModbusResponse response = master.available();

​ ​Serial.print("Holding Register values: ");

​ ​for (int i = 0; i

​ ​Serial.print(response.getRegister(i));

​ ​Serial.print(';');

​if (response) {

​ ​if (response.hasError()) {

​ ​// Response failure treatment. You can use response.getErrorCode()

​ ​// to get the error code.

​ ​Serial.print("Error code is ");

​ ​Serial.println(response.getErrorCode());

​} else {

​// Get the discrete inputs values from the response

​

​Serial.println();

}

}

}

} 

}

delay(475);

}