Exception thrown when using Serial comms

[Rufus V. Smith]

I hunted down RXTX and got ModbusPal setup to work on my Windows XP system.
I am running RS232 19.2Kbaud no parity Modbus RTU.
It will run through several transactions, but the console window will display:

Exception in thread "serial link" java.lang.ArrayIndexOutOfBoundsException: -1
at modbuspal.toolkit.ModbusTools.getUint8(ModbusTools.java:53)
at modbuspal.link.ModbusSerialLink.run(ModbusSerialLink.java:341)
at java.lang.Thread.run(Unknown Source)

and it won't process any more unless I click the "Run" button off and on, then it restarts normallly, until the
next exception.

[Rufus V. Smith]

I was browsing the source code, and my first guess is that it is not checking
received data for being a long enough message to be valid.

It creates character offsets to find the crc, etc.  by subtracting from TotalLen, which
will generate a negative index if the message was invalid (and short).

I guess I'll have to set up a Java Development environment to make some changes in my copy for now…

I'm not sure why it's getting short messages.

[CrisCV]

Hi!
First many compliments for the software!
On my PC (win7) I have the same problems for RS485 modbus comunication with the master as described by you...
Have you a compiled copy of the your modified version that you can send me, so I test and confirm the solution?

[Tamilkumaran S]

Thanks for the effort. Very useful software for testing and simulation of modbus.

I had the same issue on my PC (win7) and now fixed with small changed in the code. Here is the fix.

ModbusSerialLink.java

public void run()
{
.
.
.

                // read crc value (located in the last two bytes
                //int crcLSB = ModbusTools.getUint8(buffer, totalLen-2);

                int crcLSB = 255;
                if (totalLen > 2){
                    crcLSB = ModbusTools.getUint8(buffer, totalLen-2);
                }