# Can write to serial port, can't read from it **URL:** \ **Category:** Ignition\ **Created:** [November 16, 2010, 10:41pm UTC](https://forum.inductiveautomation.com/t/can-write-to-serial-port-cant-read-from-it/2350 "2010-11-16T22:41:33Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![chazeroo](https://avatars.discourse-cdn.com/v4/letter/c/df705f/32.png) [@chazeroo](https://forum.inductiveautomation.com/u/chazeroo)\ **Post date:** [November 16, 2010, 10:41pm UTC](https://forum.inductiveautomation.com/t/can-write-to-serial-port-cant-read-from-it/2350/1 "2010-11-16T22:41:33Z")
Hi, We need View clients to communicate with scales through the pc serial port. We’re trying to avoid using serial/EtherNet adapters. The following (RXTX-2.1-7) code under #—WRITE— works great, but I can’t get the code under #—READ— to work. No errors, just doesn’t read it. I’m testing with a second pc running HyperTerminal. I’d really appreciate any suggestions - thanks. [code]from [gnu.io](http://gnu.io) import CommPort, CommPortIdentifier, SerialPort from [java.io](http://java.io) import FileDescriptor, IOException, InputStream, OutputStream portIdentifier = CommPortIdentifier.getPortIdentifier(“COM5”) if portIdentifier.isCurrentlyOwned(): print “Error: Port is currently in use” else: commPort = portIdentifier.open(“IgnView-SerialTest”, 2000) if isinstance(commPort,SerialPort): serialPort = commPort serialPort.setSerialPortParams(9600, SerialPort.DATABITS\_7, SerialPort.STOPBITS\_1, SerialPort.PARITY\_NONE) ``` #---WRITE--- outStr = serialPort.getOutputStream() outStr.write("msg-out ") #---READ--- ``` # numBytes = -5 # readBuffer = " " # inStr = serialPort.getInputStream() # numBytes = inStr.read(readBuffer) # print numBytes # print readBuffer ``` print "done" else: print "Error: Only serial ports are handled by this example." commPort.close()[/code] ``` ---
**Author:** ![Carl.Gould](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/carl.gould/32/7262_2.png) [@Carl.Gould](https://forum.inductiveautomation.com/u/Carl.Gould)\ **Post date:** [November 17, 2010, 5:36pm UTC](https://forum.inductiveautomation.com/t/can-write-to-serial-port-cant-read-from-it/2350/2 "2010-11-17T17:36:47Z")
I don’t think I can really help you with 3rd party libraries like RXTX, which I have no experience with. I’m curious, how did you get RXTX into our software? ---
**Author:** ![chazeroo](https://avatars.discourse-cdn.com/v4/letter/c/df705f/32.png) [@chazeroo](https://forum.inductiveautomation.com/u/chazeroo)\ **Post date:** [November 17, 2010, 7:32pm UTC](https://forum.inductiveautomation.com/t/can-write-to-serial-port-cant-read-from-it/2350/3 "2010-11-17T19:32:47Z")
From [rxtx.qbang.org/wiki/index.php/In … or\_Windows](http://rxtx.qbang.org/wiki/index.php/Installation_for_Windows) (files are attached) [color=#0000FF]If you just want to run RXTX enabled programs, follow this procedure. Identify your Java Runtime Environment’s folder. For version 1.6.0, this usually is c:\Program Files\Java\jre1.6.0\_01\ Copy rxtxParallel.dll to c:\Program Files\Java\jre1.6.0\_01\bin\ Copy rxtxSerial.dll to c:\Program Files\Java\jre1.6.0\_01\bin\ Copy RXTXcomm.jar to c:\Program Files\Java\jre1.6.0\_01\lib\ext[/color] [rxtx-2.1-7-bins-r2.jar.gz](https://us1.discourse-cdn.com/inductiveautomation/original/1X/05bf42309368142e3841ed6fc7a18e9a968c1b97.gz) (589 KB) ---
**Author:** ![Carl.Gould](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/carl.gould/32/7262_2.png) [@Carl.Gould](https://forum.inductiveautomation.com/u/Carl.Gould)\ **Post date:** [November 17, 2010, 9:28pm UTC](https://forum.inductiveautomation.com/t/can-write-to-serial-port-cant-read-from-it/2350/4 "2010-11-17T21:28:17Z")
Ok fair enough. You’re still on your own with RXTX however as we can’t really support something we didn’t provide. But to give you a starting point - I’d say that you can’t use a string as a buffer like that - it doesn’t really make sense because strings are immutable. ---
**Author:** ![chazeroo](https://avatars.discourse-cdn.com/v4/letter/c/df705f/32.png) [@chazeroo](https://forum.inductiveautomation.com/u/chazeroo)\ **Post date:** [November 17, 2010, 9:54pm UTC](https://forum.inductiveautomation.com/t/can-write-to-serial-port-cant-read-from-it/2350/5 "2010-11-17T21:54:05Z")
InputStream.read is looking for a byte array. I tried readBuffer = range(20) and readBuffer = zeros(20, ‘b’) before I tried the string. No luck. ---
**Author:** ![Colby.Clegg](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/colby.clegg/32/3282_2.png) [@Colby.Clegg](https://forum.inductiveautomation.com/u/Colby.Clegg)\ **Post date:** [November 18, 2010, 1:49am UTC](https://forum.inductiveautomation.com/t/can-write-to-serial-port-cant-read-from-it/2350/6 "2010-11-18T01:49:11Z")
Well, I’m just shooting in the dark, but I google’d for creating a byte array in jython and came up with: ```auto import jarray bytearray = jarray.zeros(1024,'b') ``` I didn’t go beyond that (how to convert the jarray to different types, etc.), but hopefully that helps you get past your current block 😃 ---
**Author:** ![chazeroo](https://avatars.discourse-cdn.com/v4/letter/c/df705f/32.png) [@chazeroo](https://forum.inductiveautomation.com/u/chazeroo)\ **Post date:** [January 24, 2011, 10:00pm UTC](https://forum.inductiveautomation.com/t/can-write-to-serial-port-cant-read-from-it/2350/7 "2011-01-24T22:00:39Z")
I finally had time to play with this some more - got it to work with plain ol’ javax.comm. My next challenge is to get javax.comm & associated files to automatically deploy to clients, since javax.comm is deprecated. I’ll start digging around the Ignition Module Developers forum and see if I can figure it out. I’d appreciate any pointers to start me in the right direction - thanks! [code]from javax.comm import CommPort, CommPortIdentifier, SerialPort from [java.io](http://java.io) import FileDescriptor, IOException, InputStream, OutputStream #For this code to work: #Copy javax.comm.properties (1KB, 8/12/1999) to c:\Program Files\Java\jre6\lib\ #Copy win32com.dll (28KB, 8/12/1999) to c:\Program Files\Java\jre6\bin\ #Copy comm.jar (28KB, 8/12/1999) to C:\Program Files\Java\jre6\lib\ext #Add this to system environment variable CLASSPATH: ;C:\Program Files\Java\jre6\lib\ext\comm.jar portIdentifier = CommPortIdentifier.getPortIdentifier(“COM1”) if portIdentifier.isCurrentlyOwned(): print “Error: Port is currently in use” else: commPort = portIdentifier.open(“IgnView-SerialTest”, 2000) if isinstance(commPort,SerialPort): serialPort = commPort serialPort.setSerialPortParams(9600, SerialPort.DATABITS\_8, SerialPort.STOPBITS\_1, SerialPort.PARITY\_NONE) ``` #---WRITE--- outStr = serialPort.getOutputStream() outStr.write("msg-out") #---READ--- inStr = serialPort.getInputStream() inChr = -1 buffer = "" try: inChr = inStr.read() while ((inChr > -1) and (chr(inChr) != '\n')): buffer = buffer + chr(inChr) inChr = inStr.read() print buffer except IOException, e: e.printStackTrace() commPort.close() ``` else: print “Error: Only serial ports are handled by this example.” commPort.close() [/code] ---
**Author:** ![Carl.Gould](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/carl.gould/32/7262_2.png) [@Carl.Gould](https://forum.inductiveautomation.com/u/Carl.Gould)\ **Post date:** [January 25, 2011, 12:21am UTC](https://forum.inductiveautomation.com/t/can-write-to-serial-port-cant-read-from-it/2350/8 "2011-01-25T00:21:23Z")
Due to the nature of the java comm extension and how it has to be installed on each client machine, I don’t think you’re going to be able to automatically deploy it through Java Web Start, which is how our clients run.