Modbus RTU Communication Issue — Sending Random Float Data from Arduino Opt...

Dhinakaran

I’m working on a Modbus RTU communication setup between an Arduino Opta (as Master) and a Dacai HMI (as Slave) using RS-485.
My goal is to send random float data from the Opta to be displayed on the HMI screen.

Below i attached arduino Opta (Master) Code

1. #include <ArduinoRS485.h>
   
2. #include <ModbusMaster.h>
   
3. 
   
4. constexpr uint32_t BAUDRATE = 9600;
   
5. constexpr uint8_t HMI_SLAVE_ID = 1;
   
6. constexpr uint16_t HMI_REG_ADDR = 0x9C41;  // Dacai HMI register address
   
7. 
   
8. ModbusMaster node;
   
9. 
   
10. void setup() {
    
11.   Serial.begin(115200);
    
12.   RS485.begin(BAUDRATE);
    
13.   node.begin(HMI_SLAVE_ID, RS485);
    
14.   Serial.println("Modbus RTU Master started...");
    
15. }
    
16. 
    
17. void loop() {
    
18.   float randomFloat = random(0, 10000) / 100.0;  // Random 0.00–100.00
    
19. 
    
20.   union { float f; uint16_t words[2]; } floatData;
    
21.   floatData.f = randomFloat;
    
22. 
    
23.   node.setTransmitBuffer(0, floatData.words[0]);
    
24.   node.setTransmitBuffer(1, floatData.words[1]);
    
25. 
    
26.   uint8_t result = node.writeMultipleRegisters(HMI_REG_ADDR, 2);
    
27. 
    
28.   if (result == node.ku8MBSuccess)
    
29.     Serial.println(randomFloat);
    
30.   else {
    
31.     Serial.print("Modbus Error: 0x");
    
32.     Serial.println(result, HEX);
    
33.   }
    
34. 
    
35.   delay(2000);
    
36. }
    

复制代码

Also i have attached photo of Slave Configuration

The Opta is continuously reporting the following error:

Modbus Error: 0xE2

Can Anyone Help me to solve this ?

dctechnology

监测指令 如果不能正常显示浮点数，修改下byte order字节顺序

Dhinakaran

dctechnology 发表于 2025-10-27 15:13
监测指令 如果不能正常显示浮点数，修改下byte order字节顺序

I tried this too. This resulting the same result. There is no Modbus communication between Arduino Opta(Master) and HMI (slave)..Can u help me to solve this issue?

dctechnology

监测指令信息发我看看  

Dhinakaran

dctechnology posted on 2025-10-27 17:10:
Send me the monitoring command information.

Sorry for the delay. I've attached the screenshot of the monitoring command for your reference.