如何修改UART转Telnet代码提取Modbus十六进制帧特定字段？

Hey there, let's break down how to solve both your UART forwarding task and Modbus data extraction need clearly:

1. Complete the UART-to-Telnet Forwarding Code #

Your existing code was missing some critical pieces (like handling new client connections and proper bracket closure). Here's the polished, functional version:

// Pre-defined variables (adjust these based on your hardware setup)
HardwareSerial mySerial(1); // Use Serial1/Serial2 depending on your board
WiFiServer telnetServer(23); // Telnet default port is 23
const int MAX_TELNET_CLIENTS = 4; // Max simultaneous clients you want to support
WiFiClient telnetClients[MAX_TELNET_CLIENTS];

void setup() {
  Serial.begin(115200);
  mySerial.begin(9600); // Match your UART device's baud rate
  telnetServer.begin();
}

void loop() {
  // Handle new Telnet client connections first
  WiFiClient newClient = telnetServer.available();
  if (newClient) {
    bool clientAdded = false;
    for (int i = 0; i < MAX_TELNET_CLIENTS; i++) {
      if (!telnetClients[i] || !telnetClients[i].connected()) {
        if (telnetClients[i]) telnetClients[i].stop();
        telnetClients[i] = newClient;
        Serial.print("New Telnet client from: ");
        Serial.println(newClient.remoteIP());
        clientAdded = true;
        break;
      }
    }
    if (!clientAdded) {
      newClient.println("Maximum clients reached. Try later.");
      newClient.stop();
    }
  }

  // Read UART data and forward to all connected Telnet clients
  if (mySerial.available()) {
    size_t dataLen = mySerial.available();
    uint8_t uartBuffer[dataLen];
    mySerial.readBytes(uartBuffer, dataLen);

    // Forward to each active client
    for (int i = 0; i < MAX_TELNET_CLIENTS; i++) {
      if (telnetClients[i] && telnetClients[i].connected()) {
        telnetClients[i].write(uartBuffer, dataLen);
        delay(1); // Small delay to prevent data loss on client side
      }
    }
  }
}

Key Improvements: #

• Added full client connection management (accept new clients, replace disconnected ones, handle max client limit)
• Fixed variable scoping and bracket closure issues from your original snippet
• Made the code more readable with descriptive variable names

2. Extract the 4th and 5th Hex Pairs from Modbus Data #

Your target Modbus frame is 10 03 02 01 1F 04 1F — remember that byte arrays are 0-indexed, so:

• 4th hex pair (01) = index 3 in the byte array
• 5th hex pair (1F) = index 4 in the byte array

Here's how to extract and use these values, integrated right into the UART forwarding logic:

// Insert this inside the UART data handling block (after reading uartBuffer)
if (dataLen >= 5) { // Ensure we have at least 5 bytes to avoid index out of bounds
  uint8_t fourthHexByte = uartBuffer[3]; // 0x01
  uint8_t fifthHexByte = uartBuffer[4]; // 0x1F

  // Optional: Combine into a 16-bit value (since Modbus uses big-endian)
  uint16_t combinedValue = (fourthHexByte << 8) | fifthHexByte; // 0x011F = 287 in decimal

  // Example usage: Print the extracted values
  Serial.print("Extracted 4th hex byte: 0x");
  Serial.println(fourthHexByte, HEX);
  Serial.print("Extracted 5th hex byte: 0x");
  Serial.println(fifthHexByte, HEX);
  Serial.print("Combined 16-bit value: 0x");
  Serial.println(combinedValue, HEX);
}

Notes: #

• Always check the data length first to prevent crashes from accessing invalid array indices
• The combined value uses left shift (<< 8) to move the 4th byte into the high 8 bits, then combines with the 5th byte using bitwise OR (|) — this matches Modbus's big-endian byte order
• You can modify the usage logic to send just this extracted value to Telnet clients, store it, or use it for further processing

内容的提问来源于stack exchange，提问作者dadex