Troubleshooting method of communication between panel and PLC

If the panel cannot communicate with the S7 plc, the typical phenomenon is that ##### is displayed in the IO field on the screen. Unable to establish a communication connection with the PLC, please follow the steps below to troubleshoot:

1. Check the cable you are using

• For PPI/MPI/Profibus/communication with S7-200/300/400, MPI cable can be used (pins at both ends correspond to: 3-3, 4-4, 5-5, 8-8) Or Profibus cable (the corresponding pins at both ends are: 3-3, 8-8).
• It is recommended to use Siemens purple Profibus cable and Profibus bus connector (or DP connector).
• You can use self-made shielded twisted-pair cables, but the shielding and grounding issues should be properly handled. Siemens does not make any kind of commitment or guarantee for self-made cables.
• If you use DP connectors to connect multiple stations on the network, please be sure to pay attention to the status of the DP connector terminal resistance: the connectors at both ends of the network are ON, and the middle one is OFF; the connectors at both ends are connected to the cable. Figure 1.

Figure 1

2. Check and confirm the setting of PLC communication port

• Baud rates must be the same.
• Station addresses cannot conflict.
• Choose the same protocol.

3. Check the communication settings in Portal and WinCC flexible

• The address of the same level of communication should be consistent with the actual station address of the PLC. Note: If it is S7-300/400, you need to set the slot number (the slot number must be consistent with the CPU slot number in the Step7 hardware configuration).
• The address of OP must be unique and cannot be repeated with the address of any device in the network.
• The baud rate must be consistent with the PLC setting.

Figure 2

• The configuration file Profile must be consistent with the protocol used by the network. Note: When communicating with S7-200, the panel can have multiple options, and the PLC is protocol-adaptive, so there is no need to set it in MicroWin, just set the port number and baud rate in the system block of MicroWin.

Figure 3

• Select “Only master on bus”.

4. Check whether the communication port on the back of the panel is used correctly

• The IF1B port is used for PPI/MPI/Profibus communication with S7-200/300/400, and the dial switch of IF1B on the back of the panel should keep the factory setting and turn to OFF.

5. Check the system alarm information

In order to further eliminate communication faults, during debugging, an enhanced object “alarm view” can be added to the “template” of the touch screen to view system alarm messages. Check the “System” alarm category in the “General” attribute “Alarm Event”.

Figure 4

After the items in the panel are activated and running, you can view the number of the system alarm message.

Figure 5

In the configuration software, modify the “Workbench” of “Settings” under the menu “Options” to: display all items. “System Events” will be displayed in the directory tree “Alarm Management”.

Figure 6

Through the “system event” in the “alarm management”, you can view the system alarm messages corresponding to all alarm numbers. In this way, after the corresponding alarm message is determined according to the message number, specific problems can be solved in a targeted manner.

Figure 7

Please refer to the appendix in the following link for the solutions corresponding to various message numbers: A.2 System alarm 26248558

Figure 8

In addition, it is necessary:
• power on the panel and PLC again;
• change a new Profibus cable.

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