How to Configure and Communicate with Serial Ports (RS-232, RS-422): Setting Baud Rate & Programming in Java, C/C++, Unix Shells, Windows/Hyperterminal

ls /dev/tty* | grep -E "ttyUSB|ttyS"  # USB: ttyUSB0; Hardware: ttyS0  

stty -F /dev/ttyUSB0 9600 cs8 -cstopb -parenb -ixon  # -ixon disables XON/XOFF flow control  

#include <windows.h>  
#include <stdio.h>  
 
int main() {  
    HANDLE hCom;  
    DCB dcb;  
    BOOL fSuccess;  
 
    // Step 1: Open the serial port (COM3)  
    hCom = CreateFile(  
        "COM3",                  // Port name  
        GENERIC_READ | GENERIC_WRITE,  // Read/write access  
        0,                       // No sharing  
        NULL,                    // Default security  
        OPEN_EXISTING,           // Open existing port  
        0,                       // Non-overlapped I/O  
        NULL                     // No template  
    );  
    if (hCom == INVALID_HANDLE_VALUE) {  
        printf("Error opening COM3: %lu\n", GetLastError());  
        return 1;  
    }  
 
    // Step 2: Configure port settings (9600, 8N1)  
    fSuccess = GetCommState(hCom, &dcb);  
    if (!fSuccess) { printf("GetCommState failed: %lu\n", GetLastError()); return 1; }  
 
    dcb.BaudRate = CBR_9600;    // 9600 baud  
    dcb.ByteSize = 8;           // 8 data bits  
    dcb.StopBits = ONESTOPBIT;  // 1 stop bit  
    dcb.Parity = NOPARITY;      // No parity  
    dcb.fOutX = FALSE;          // Disable XON/XOFF  
    dcb.fInX = FALSE;  
 
    fSuccess = SetCommState(hCom, &dcb);  
    if (!fSuccess) { printf("SetCommState failed: %lu\n", GetLastError()); return 1; }  
 
    // Step 3: Send data  
    char* txBuffer = "Hello from Windows!\n";  
    DWORD bytesWritten;  
    fSuccess = WriteFile(hCom, txBuffer, strlen(txBuffer), &bytesWritten, NULL);  
    if (!fSuccess) { printf("WriteFile failed: %lu\n", GetLastError()); return 1; }  
    printf("Sent %lu bytes\n", bytesWritten);  
 
    // Step 4: Read data (example)  
    char rxBuffer[1024];  
    DWORD bytesRead;  
    fSuccess = ReadFile(hCom, rxBuffer, sizeof(rxBuffer)-1, &bytesRead, NULL);  
    if (fSuccess && bytesRead > 0) {  
        rxBuffer[bytesRead] = '\0';  
        printf("Received: %s\n", rxBuffer);  
    }  
 
    // Step 5: Close the port  
    CloseHandle(hCom);  
    return 0;  
}  

#include <stdio.h>  
#include <fcntl.h>  
#include <unistd.h>  
#include <termios.h>  
 
int main() {  
    int fd;  
    struct termios tty;  
 
    // Step 1: Open the port (/dev/ttyUSB0)  
    fd = open("/dev/ttyUSB0", O_RDWR | O_NOCTTY | O_NONBLOCK);  // O_NONBLOCK for non-blocking read  
    if (fd < 0) { perror("Error opening port"); return 1; }  
 
    // Step 2: Configure port (9600, 8N1)  
    if (tcgetattr(fd, &tty) != 0) { perror("tcgetattr failed"); return 1; }  
 
    // Set baud rate (input/output)  
    cfsetospeed(&tty, B9600);  
    cfsetispeed(&tty, B9600);  
 
    tty.c_cflag &= ~PARENB;   // No parity  
    tty.c_cflag &= ~CSTOPB;   // 1 stop bit  
    tty.c_cflag &= ~CSIZE;    // Clear data bits  
    tty.c_cflag |= CS8;       // 8 data bits  
    tty.c_cflag &= ~CRTSCTS;  // Disable hardware flow control  
    tty.c_cflag |= CREAD | CLOCAL;  // Enable receiver, ignore modem controls  
 
    // Raw input (no line buffering)  
    tty.c_lflag &= ~ICANON;  
    tty.c_lflag &= ~ECHO;     // Disable echo  
 
    // Apply settings immediately  
    if (tcsetattr(fd, TCSANOW, &tty) != 0) { perror("tcsetattr failed"); return 1; }  
 
    // Step 3: Send data  
    char* txBuffer = "Hello from Unix!\n";  
    int bytesWritten = write(fd, txBuffer, strlen(txBuffer));  
    if (bytesWritten < 0) { perror("write failed"); return 1; }  
    printf("Sent %d bytes\n", bytesWritten);  
 
    // Step 4: Read data (non-blocking)  
    char rxBuffer[1024];  
    int bytesRead = read(fd, rxBuffer, sizeof(rxBuffer)-1);  
    if (bytesRead > 0) {  
        rxBuffer[bytesRead] = '\0';  
        printf("Received: %s\n", rxBuffer);  
    }  
 
    // Step 5: Close port  
    close(fd);  
    return 0;  
}  

<dependency>  
    <groupId>com.fazecast</groupId>  
    <artifactId>jSerialComm</artifactId>  
    <version>2.10.3</version>  
</dependency>  

import com.fazecast.jSerialComm.SerialPort;  
 
public class SerialCommExample {  
    public static void main(String[] args) {  
        // Step 1: List available ports  
        SerialPort[] ports = SerialPort.getCommPorts();  
        System.out.println("Available ports:");  
        for (int i = 0; i < ports.length; i++)  
            System.out.println(i + ": " + ports[i].getSystemPortName());  
 
        // Step 2: Open the first port (adjust index as needed)  
        SerialPort port = ports[0];  
        if (!port.openPort()) {  
            System.err.println("Failed to open port");  
            return;  
        }  
 
        // Step 3: Configure port (9600, 8N1)  
        port.setBaudRate(9600);  
        port.setNumDataBits(8);  
        port.setNumStopBits(SerialPort.ONE_STOP_BIT);  
        port.setParity(SerialPort.NO_PARITY);  
        port.setFlowControl(SerialPort.FLOW_CONTROL_DISABLED);  
 
        // Step 4: Send data  
        String txData = "Hello from Java!\n";  
        byte[] txBuffer = txData.getBytes();  
        port.writeBytes(txBuffer, txBuffer.length);  
        System.out.println("Sent: " + txData);  
 
        // Step 5: Read data (blocking)  
        byte[] rxBuffer = new byte[1024];  
        int bytesRead = port.readBytes(rxBuffer, rxBuffer.length);  
        if (bytesRead > 0) {  
            String rxData = new String(rxBuffer, 0, bytesRead);  
            System.out.println("Received: " + rxData);  
        }  
 
        // Step 6: Close port  
        port.closePort();  
    }  
}