Hello jinn;

The TP177 is not part of the hardware configuration of the CPU, normally. Please check the Profibus configuration.

That is because a TP (or any HMI panel from Siemens) does not act as a DP-slave, but as a Profibus-DP master Class 2.

See there FAQs from Profibus.com:

Why are Class1 and Class 2 masters different?

Why are Class 1 and Class 2 masters different?

A Class 1 master can communicate actively only with its configured slaves and is able to communicate in a passive way with a Class 2 master. The class 2 master is the 'supervisory' device. It can communicate with Class 1 masters, their slaves and its own slaves for configuration, diagnostic and data/parameter exchange purposes.

As such, it captures the Profibus token from the CPU in order to interrogate other masters and slaves on the network when it needs to exchange data with any of them, then releasing it back to the other master(s) on the network.

So removing it should not cause a crisis on the bus, as removing a slave could.

Try this: simply start by cutting power from the TP. The bus should remain stable. Then you can disconnect the Profibus connector from the unpowered TP. If you leave the connector on the Profibus line (without modifying the electrical connections or the terminator position) then the PLC should continue to poll all its configured slaves as normal. It will simply no longer exchange the token with the TP during its cycle, and it should adjust without setting off alarms, same as if you would remove a PC programming unit (another type of Profibus master class 2)from the bus.

Leaving an unconnected Profibus connector is not without electrical risks of course, and this should be considered a (very) short-term solution. You should at minimum protect the connection pins (cap or tape the connector, place it in a nearby cabinet) until such time as a planned shutdown allows you to change the Profibus cable between the IO module and the OLM that are on both sides of the present TP (as shown on your sketch).

So I believe that a Profibus active terminator would not be necessary at this point.

Hope this helps,

Daniel Chartier

Hello jinn;

What error status do you get, and on what PLC do you get it (or both)?

What LEDS are active, on which PLC?

What are the diagnostic buffer entries that appear for this situation?

Hope this helps,

Daniel Chartier