Java serial port reading hex values

Question

I want to write some hex data to the serial port and read back some data. I have a problem in the reading (reads nothing) could someone help???

import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.DataInputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Map;

public class Test {
    public static void main(String[] args) throws IOException {
        char c='s';
        ProcessBuilder builder = new ProcessBuilder("c:\\windows\\system32\\mode.com", "portname", 
            "baud=115200", "parity=n", "data=8","stop=1");
        Map<String, String> environ = builder.environment();
        String portname="com6";
        final Process process = builder.start();
        String x="";
        byte data[] = {(byte)0xF5, (byte)0xfa, (byte)0x01, (byte)0x01, (byte)0x00, (byte)0x00, (byte)0xfe, (byte)0x0f};
        FileOutputStream fos = new FileOutputStream(portname );
        BufferedOutputStream bos = new BufferedOutputStream( fos );
        fos.flush();
        fos.write( data);
        fos.close();
        bos.close();
        FileInputStream fstream1 = new FileInputStream(portname);
        DataInputStream in = new DataInputStream(fstream1);
        BufferedReader br = new BufferedReader(new InputStreamReader(in));
        int n = 0;
        while ((n =(char) in.read()) !=-1 ){
            System.out.println((char)fstream1.read());
        }
    }
}

Why not use a java serial library, like jSSC, RxTx or xidobi ? — Chriss
– Chriss, Commented Dec 16, 2015 at 11:57

Jan · Accepted Answer · 2015-12-16 10:44:34Z

0

You pass in a string "portname" istead of the variable portname. See the following change to the code:

String portname="com6"; //Move it here
ProcessBuilder builder = new ProcessBuilder("c:\\windows\\system32\\mode.com", 
             portname, //instead of "portname"
           "baud=115200", "parity=n", "data=8","stop=1");
Map<String, String> environ = builder.environment();

After that change, I had my system block on the read() - because I have nothing connected to that port.

You read from both streams - and that way you skip bytes. Try it with just the most basic streams first:

 try{
   FileOutputStream fos = new FileOutputStream(portname ); 
   fos.write( data);
   fos.flush();
   fos.close();

   FileInputStream    fstream1 = new FileInputStream(portname);
   int n = in.read();
   while (n != -1 ){
       System.out.println(n);
       n = in.read();
   }
   System.out.println("Reading ended");
 } catch(Exception e) {
    e.printStackTrace();
 }

That should at least get back what you've written.

edited Dec 16, 2015 at 10:44

answered Dec 15, 2015 at 14:08

Jan

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5 Comments

Jan Over a year ago

well all that code does is write some bytes to a file and then read it back though - doesn't connect to serial port in any way

Jan Over a year ago

Check again please - with the try-catch around your file logic. I think there might be an Exception involved

Jan Over a year ago

and again no error, no nothing? can you share updated code?

javac31 Over a year ago

It just reads -1 the end of the stream no other data are read

Jan Over a year ago

See my latest edit - you might not even be connected to the port.

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