Modbus TCP/IP on PC

Can anyone recommend a good freeware or low cost routine I can run on my PC to perform modbus TCP/IP read write polling? I just need it for some diagnostic purposes.

ModScan will do that, see link below

http://www.google.com/#hl=en&cp=5&g....,cf.osb&fp=9fd4d23f4504bf41&biw=1592&bih=803

Some free ones:

http://www.azeotech.com/index.php
The software includes a free demo that does modbus reads/writes. Serial or ethernet.

http://deltacompsys.com/files/tcpdemo.zip
Good little tool - has some basic stats. Ethernet only, includes some other protocols too - seemed to be a great companion to a Digi One IAP - the protocol support seems to match pretty well.

http://www.redlion.net/Support/Downloads/SoftwareLibrary/Crimson3.html
Use emulator from PC - most drivers work so can test many things with the huge selection of drivers. A spare Modular controller laying around is a huge help for longer term tests, but if you only need a few minutes, the demo works well.

I concur with Mickey; ModScan32 from WinTech Software is my go-to shareware tool for Modbus RTU and Modbus/TCP testing.

For very quick tests it's free, and the shareware license is more than worth the money.

Ken Roach said:

I concur with Mickey; ModScan32 from WinTech Software is my go-to shareware tool for Modbus RTU and Modbus/TCP testing.

For very quick tests it's free, and the shareware license is more than worth the money.

Click to expand...

I concur, too.

Simply Modbus has one advantage - it can display a different word format for each register/address, whereas Modscan shows only one word format per window. Modscan's licensed version will open multiple windows (not sure about unlicensed version) where each window can show its own word format. But there have been times when it's convenient to see multiple variables, some with different word formats on the same page.

For the peanuts either costs, they're great troubleshooting tools.

Two other great free tools for the Modbus experimenter:

Chipkin Automation Systems has a "Modbus Parser", that will decode Modbus frames. Big time saver when you are looking through a hex dump.

http://www.chipkin.com/cas-modbus-rtu-parser

Lammert Bies has a fantastic detailed site regarding serial principles and practice, and I use his online CRC generator when I'm working with Modbus and DF1:

http://www.lammertbies.nl/comm/info/crc-calculation.html

I really like modbus poll.

Driving this thread even further off topic, if you're into Modbus, check out a control.com thread.
http://www.control.com/thread/1323333495
The one to read is Gerry's reply to the Modbus issue where the floating point value for the same variable differed slightly when read by two different Modbus masters.

Gerry did an analysis with an example to show that one of the Masters had a one offset addressing issue (combined with a swapped hi/low order), where a two register floating point 03 'read' function reads the first register assigned to one variable, the 2nd register from a register assigned to a different variable.

The resulting floating point value looks to be reasonable, but it is off, it is not the correct value.

Thank you all for your responses.

My situation right now is that I have a PLC acting as a Modbus TCP/IP server to two slave servo drives. What is happening is every now and then an interruption in communication will occur, and the communication between the PLC and one or both of the servo drives will hang. The only way I can get it to restart is by rebooting the servo. Rebooting the PLC has no effect. What I believe is happening is that the drive is leaving the socket "half open". After that, all the socket open and close requests from the PLC appear to be ignored. The drive continues to communicate ethernet, (via my PC), but refuses to accept any new requests from the PLC until rebooted. I guess I am looking for the tool that gives me the most control over everything (open sockets, closing sockets, timing etc.). Modscan is working fine, but doesn't appear to be letting me "behind the scenes" so to speak.

I think I am now going to give the chipkin thing a try that Ken suggested. It looks as though they have a TCP version as well.

Thanks again everyone for your suggestions.

DamianInRochester said:

PLC acting as a Modbus TCP/IP server to two slave servo drives.

Click to expand...

FYI, convention calls the modbus master the 'client'; the modbus slaves are the 'servers'.

Flashback

danw said:

FYI, convention calls the modbus master the 'client'; the modbus slaves are the 'servers'.

Click to expand...

The first time I worked with Modbus TCP those terms thru me. My thinking was servers would be like a server on a PC network which is basically the master and the client would be the slaves like a remote terminal. My first attempt at a setup was quite comical.

Dan, Thank you for the correction. I always mess that up.