Problem in Modbus Master Simulation Tools


Thread Starter

Rupak Shrestha

I want to use serial communication with Modbus RTU frame and Modbus TCP/IP frame for communicating Storage Energy Management System with my computer. So, I'm using free softwares like Simply Modbus Master 7.1 and TCP Client 7.1 (, and Modbus Poll(from

But with the Simply Modbus software, I'm not able to get the response from the slave device. Also from the Modbus Poll, I'm always getting the Time-out Error. I studied their manuals but I'm not able to figure out the problem. I want to know how can I fix this problem and whether other free simulating softwares are available or not. Please feel free to contact me.

Thank you in advance.
>>...with the Simply Modbus software, I'm not able to get the response from the slave device. <<

If you are using Windows 7, you must set XP compatibility on the exe file to allow the Simply Modbus software to access the serial port.

Lynn August Linse

Well, if 3 different test tools don't work, a fourth wouldn't work either.

So one of these is your problem:
1) your device is broken

2) your device is not really Modbus

3) your cabling is wrong

4) slave address or baud rate is non-standard - perhaps NOT the default, so you might need to try lots of combinations.
It sounds like you just don't have a connection. RS-485 has some issues.

The A/B or (+)/(-) lines are labeled differently, depending on manufacturer. One major European manufacturer labels one way in one division, the opposite in another division.

So you should always try swapping the A/B or (+)/(-) lines when working with RS-485. If the wiring is reversed, you won't get a connection, but the line drivers will not be damaged.

If you have the option to use ethernet, I'd use that first to get familiar with the master programs, because its connection does not have the A/B line issue, nor the baud rate/word size/parity issue.