Siemens TI-505 Remote I/O


Thread Starter


I'm not familar with Siemens PLCs at all. If I disconnect a Profibus remote I/O cable from the PLC to my remote junction box, will it fault the PLC processor? I'm trying to disconnect an entire remote junction box while on-line but do not know if it will fault the processor.

Depends on which PLC you're using as the Profibus master. If it's an S7 running with TI-505 RIO, whether or not it will fault will depend on whether or not you have some particular OB's defined. I think it's one or more of 82, 85, or 121 IIRC. If the programmer didn't want it to fault, he'd load empty versions of those OB(s), or ones that do something else other than fault, like turn on an alarm light for example.

If you're using a 555 or other TI PLC as the Profi master, I don't know what it will do. I never used a 505 as a Profi master.
It should just give a minor fault that gives an error, not a major one that would shut down the processor. It would be silly to design a PLC that faulted and shut down when Remote I/O failed. Although I have not tested your case, the PLC does not create a major fault when a regular Remote I/O rack fails.

If you are really worried, contact CTI (they make TI clones) or refer to their online pdf manuals.


Gilles Allard

As Steve Myres mentioned the answer depends on the type of CPU you use.

If you use a 5x5 CPU, it will not fault. However:

- if there are other stations on the bus, they may be affected if the line terminator is in the connector you disconnect.

- the PLC program will receive zeroes for all input signals coming from the disconnected stations. Depending on the PLC logic, it may create side-effects.
Your remote I/O block will definitely have Bus Fault. BF led would go red. CPU should not go into stop mode, unless some profibus dp or some other organization block is configured to interrupt operation of CPU.