Hello Everyone,

I hope this message finds you well.

I am in need of assistance regarding the communication over Profibus between a PLC and a slave/module. I believe I have explored many options, but I am still encountering difficulties and would appreciate your expertise.

I am currently working with a PLC 1200 (CPU 1211C-RC/DC/RLY) using TIA Portal version 17, and I have an additional module that I can connect to my Profibus interface. I downloaded the GSD file from the manual that came with my module (Reovib MFS 268 DB) and have configured the address according to the specifications of the module.

Despite my efforts using SFC 14 and SFC 15, I have not been successful. Additionally, when attempting to download, I receive an error message indicating that the slave is not reachable.

I would greatly appreciate any help or insights you may have on resolving this issue.

Thank you in advance for your assistance!

Best regards,
magnus

Hello Daniel,

First of all, sorry for the very late reply — I have been on vacation, which is why I haven't been able to respond earlier.
plus I didn’t expect to get a reply that fast

Thank you for your detailed reply and for pointing me to the manual and the video guide for the CM 1243-5 module.

To clarify, I am indeed using the CM 1243-5 module as a Profibus master together with my S7-1200 PLC (CPU 1211C DC/DC/RLY), and I'm working in TIA Portal v17. I’ve downloaded the correct GSD file for the Reovib MFS 268 device and set the Profibus address according to the manual.

However, when I try to download the configuration, I still receive a “slave not reachable” error. I've attempted communication using SFC 14 (DPWR_DAT) and SFC 15 (DPRD_DAT), but I now understand that these instructions were primarily intended for S7-300/400 systems using Step 7 (v5.x).

For my setup with S7-1200 + CM 1243-5 in TIA Portal v17, I realize these instructions might not be necessary or even compatible in the same way — and that TIA Portal likely handles the Profibus communication differently, using the I/O mapping or other configured interfaces.

As I understand it now, I likely don’t need to use SFC 14 and 15 directly with a 1200-series CPU in TIA Portal when communicating with a Profibus slave. I suspect I should be reading and writing data via the configured input/output areas instead, once the module is properly recognized and reachable.

If you could confirm this understanding or let me know what I might be missing in the hardware setup or network configuration, I would really appreciate it.

P.S. I tried to send some pictures, but I couldn’t include them — sorry!

Thanks again for your time and help!

Best regards,
Magnus

Firstly you need to get the communication working, before you can start reading/writing data to the device.

In a Profibus network, it's crucial to have the end termination of the bus ON in both ends of the cable, for the bus to work correctly. If the end termiantion is OFF in the node where the bus ends, that device will not have a working communication.

Hello Hati,

Thanks again for your support and insights.

To clarify a few more things based on your input:

• Regarding termination, it is enabled at both ends of the Profibus line — one at the CM 1243-5 module, and one at the last Reovib slave.
• Additionally, I’ve tested the Profibus cable using a diagnostic tool that checks for signal integrity and line breaks — and it confirmed that the cable is OK and that there is a valid signal on the line.

Despite this, I still receive the "slave not reachable" error when downloading or attempting to bring the bus online.

At this point, I’m wondering if the issue could be:

1. A mismatch between the module’s configured address and what the Reovib unit is actually set to,
2. Or a possible problem with how the Reovib unit is configured internally (e.g. DIP switches or parameter settings),
3. Or maybe something subtle in the device configuration within TIA Portal.

Thanks again for taking the time to help — it’s really appreciated!

Best regards,
Magnus

Just na idea what could also cause this:  if you terminate the cable ends on the profibus connectors (as opposed to separate terminators), you need to check whether the end stations have the profibus cable inserted in the correct slot on the connector (both ends must be in the incoming slot). If an end is inserted in the outgoing slot and it is terminated you cut off that station. I've found this quite a common problem when commissioning.