LOGO! BM 24CE - Problems with Modbus

Hello everyone!

I'm working on a project that also includes the integration of a PLC, more specifically I was provided with a LOGO! BM 24CE with model number 6ED1052-1CC08-0BA1. Significant communication difficulties have emerged, even with an apparently correct configuration using the LOGO! Soft Comfort software. The main obstacle concerns the inability to establish a connection using the Modbus/TCP protocol: even though the dedicated option was activated and a test program was loaded, checks with nmap indicate that port 502, which is essential for Modbus/TCP, is closed.

Even by configuring a dedicated Modbus server or setting the device to accept connections from any IP, communication is not established. Browsing this forum and reading various discussions, it seems that this issue is recurring. How could I solve it?

I thank everyone who can help me out!

Hello, thank you for your reply.

I'll explain a little how I did it. The steps are these:

• I created a new network project on the software mentioned earlier
• I added a new device and also connected it
• Then by checking the device properties I enabled Modbus/TCP access (in fact there was a warning saying that port 502 would be open)
• Created a test program (simple input -> output)
• Loaded the program on the plc

As mentioned before, checking with nmap the port was closed.

Did I do something wrong?

I was told it was an issue with DHCP being enabled to on the same IP as the unit but couldn't see how this could be true and haven't been able to sort it out so far (6 months down the line).

Still can't connect to Modbus, except when directly plugged into the PLC network port.

I can confirm I can connect to the PLC by typing in the IP address and the details about Open Source files is displayed.

So whatever it is seems peculiar to Modbus.

I realised this, and have never done this.

My post was about a supposed issue when the IP address of the PLC is within the DHCP range of the network.

I questioned this at the time, because I've never heard of anything like this in my career in automation, it simply didn't make any sense to me. Basically you have to change the network infrastructure to suit Siemens, should you choose to use one of their PLCs.

This issue has been refuted by Siemens help desk since I originally posted, but I've yet to find a solution.

Hi,

one time is always the first time hearing some thing new.

The issue with fixed IP-adr. and WiFi IP-range is not a Siemens Issue. It is an issue in the router's. Some router strictly seperate wired IP-adress range and DHCP adress range, some router do not seperate strictly.

However: If your Modbus test works if the LOGO! is directly connected to your PC and it doesn't work if LOGO! is connected to your IP-Network, then your network configuration needs to be configured right.

Here the DHCP issue can help. 

If you don't get it to work, ask your IT admin. 

Hope this helps