Hello everyone. I would really appreciate your help with this problem i am facing. I'm newbie in Arduino.
I am trying to read sensor parameter via RS485 using modbus RTU but unable to do. I have seen tutorial & read in many forum but didn't success.
Modbus mapping for the sensor: https://www.emerson.com/documents/automation/modbus-mapping-assignments-for-transmitters-en-65522.pdf
I am using MAX485 - TTL UART to RS485 Converter Module: https://core-electronics.com.au/ttl-uart-to-rs485-converter-module.html
I have been checking parameter of the sensor using manufactures software. Here is the the parameter:
- Baudrate: 38400
- ID Slave: 4
- Parity: None
- Stop bits: 1
Then I want to monitor sensor temperature. The address of holding register is: 0251. When I check from serial monitor, modbus communication is failed and the address is change to 169. I think, I can not write the register with prefix "0".
Here is my code:
#include <ModbusMaster.h>
#define baudrate 38400
#define timeout 100
#define polling 100
#define retry_count 10
ModbusMaster node;
#define MAX485_DE 2
#define MAX485_RE_NEG 3
#define ID_meter 4
#define Total_of_Reg 1
#define Reg_E 0251 // Sensor temperature register
uint16_t Reg_addr[1] = {
Reg_E
};
float DATA_METER [Total_of_Reg] ;
void preTransmission()
{
digitalWrite(MAX485_RE_NEG, 1);
digitalWrite(MAX485_DE, 1);
}
void postTransmission()
{
digitalWrite(MAX485_RE_NEG, 0);
digitalWrite(MAX485_DE, 0);
}
//------------------------------------------------
// Convent 32bit to float
//------------------------------------------------
float HexTofloat(uint32_t x)
{
return (*(float*)&x);
}
uint32_t FloatTohex(float x)
{
return (*(uint32_t*)&x);
}
//------------------------------------------------
float Read_Meter_float(char addr , uint16_t REG)
{
float i = 0;
uint8_t result,j;
uint16_t data[5];
uint32_t value = 0;
node.begin(ID_meter,Serial);
node.preTransmission(preTransmission);
node.postTransmission(postTransmission);
result = node.readHoldingRegisters(REG,4); ///< Modbus function 0x03 Read Holding Registers
delay(500);
if (result == node.ku8MBSuccess)
{
for (j = 0; j < 5; j++)
{
data[j] = (node.getResponseBuffer(j));
}
value = data[1];
value = value << 16;
value = value + data[1];
i = HexTofloat(value);
Serial.println("Connect modbus Ok.");
return i;
} else
{
Serial.print("Connect modbus fail. REG >>> "); Serial.println(REG); // Debug
delay(1000);
return 0;
}
}
void GET_METER()
{ // Update read all data
delay(1000);
for (char i = 0; i < Total_of_Reg ; i++)
{
DATA_METER [i] = Read_Meter_float(ID_meter, Reg_addr[i]);
}
}
void setup()
{
Serial.begin(baudrate, SERIAL_8N1);
Serial.println(F("Test"));
pinMode(MAX485_RE_NEG, OUTPUT);
pinMode(MAX485_DE, OUTPUT);
// Init in receive mode
digitalWrite(MAX485_RE_NEG, 0);
digitalWrite(MAX485_DE, 0);
}
void loop()
{
//float x = Read_Meter_float(ID_meter,Reg_Volt);
GET_METER();
Serial.println();
Serial.print("Data = "); Serial.println(DATA_METER[0]);
}
Please help me out and thanks in advance.
And please let me know if any other information I need to provide. Thank you
