If the panel and S7 PLC are not communicating, a common symptom is that the IO field displays "#####" in the screen. If you're unable to establish a communication link with the PLC, follow these steps to troubleshoot:
1. Check the cable used
• For PPI/MPI/Profibus communication with S7-200/300/400, use an MPI cable (pins at both ends correspond to: 3-3, 4-4, 5-5, 8-8) or a Profibus cable (stitches at both ends correspond to: 3-3, 8-8).
• It's recommended to use Siemens Purple Profibus cables and Profibus bus connectors (or DP connectors).
• You can also use a homemade shielded twisted pair cable, but proper shielding and grounding must be ensured. Siemens does not guarantee or support homemade cables.
• When using a DP connector to connect multiple stations on the network, ensure the terminating resistor is ON at both ends of the network and OFF in the middle. See Figure 1.
Figure 1
2. Check and confirm the settings of the PLC communication port
• The baud rate must be consistent across all devices.
• Ensure there are no conflicting station addresses.
• Use the same communication protocol on both ends.
3. Check communication settings in Portal and WinCC Flexible
• The address of the communication partner must match the actual station address of the PLC. Note: For S7-300/400, set the slot number to match the one in Step7 hardware configuration.
• The OP’s address must be unique and not conflict with any other device on the network.
• The baud rate should match the one configured on the PLC.
Figure 2
• The profile should match the protocol used on the network. When communicating with S7-200, the panel has multiple options, and the PLC is protocol-adaptive. No need to set it in MicroWin—just configure the port number and baud rate in the system block.
Image 3
• Select “Unique master on busâ€.
4. Verify the correct usage of the panel’s communication port
• The IF1B port is used for PPI/MPI/Profibus communication with S7-200/300/400. The IF1B dial switch on the back of the panel should be factory-set and turned OFF.
5. Review system alarm information
To further identify communication issues, add the “Alarm View†object to the “template†of the touch screen during commissioning. This allows you to view system alarm messages. Check the “System†category under the “General†property “Alarm Eventsâ€.
Figure 4
After activating the project on the panel, you can view the number of system alarm messages.
Figure 5
In the configuration software, go to “Options†> “Settings†> “Workbench†and select “Display all items.†“System Events†will appear under the “Alarm Management†directory tree.
Figure 6
You can view all system alarm messages through “System Events†in “Alarm Management.†Once the corresponding alarm message is identified based on the message number, you can resolve the issue more effectively.
Figure 7
For solutions related to specific message numbers, refer to the appendix in this link: A.2 System Alarm 26248558.
Figure 8
Additionally, make sure to:
• Power up both the panel and the PLC.
• Replace the Profibus cable with a new one if necessary.
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