Detecting communication fault between a SIMATIC PLC and HMI station

Hi,

I have a SIMATIC 416-2 CPU connected to a MP 377 WinCC touch screen via MPI cable.

How do I detect a communication fault on the MPI cable (between the PLC and the touch panel)

1. in the plc program?

2. in the WinCC application?

Hi,

I have some suggestions that may seem a little crude:-

1) you could use a bit that is set in the PLC and reset in the HMI. then in the rung above it have a timer or counter and if it is on for more than x scans or seconds the fault is detected. and viceversa for the HMI.

2) an alternative to that is to always change a number in the other station eg winCC always changes a value in the PLC. Then if the number stays the same for a period there is a fault.

These ofcourse also detect if the system has stopped running.

3) Depending how the bus is configured you could use some of the OB blocks that are called when communication faults occur. I can't remember them but it might be OB85,86,87 or OB121,122 from memory.

Hope this helps, I'm sure you'll get a better response soon.

Regards
David Askew
www.plccables.com.au
www.fast-automation.com

If your WinCC Flexible is recent (i.e. 2008 + SP1), then it has become very easy.
You have now access to certain System events, including if the online connection is etablished or is disconnected.
In WinCC Flexible go to Options .. Settings .. Workbench .. Project View Settings, then select Display all items.
You can then go to the project tree under Alarm Management .. System Events and find the events no 140000 Connection Established and 140001 Connection Disconnected. Add event actions to set an internal tag "Online_OK" to 1 and 0 for example.
With the "online_OK" tag, program for example an indicator with green for online OK, and red for not OK for example.

Prior to 2008 + SP1 there were some more cumbersome methods. You dont want to use these if you can avoid it.

edit:
Btw, why dont you use ethernet with the panel ?
Both PLC and Panel have ethernet, so that is what I would do if I were you.

Thank you.

Here's SIEMENS' response to question 1 for whoever may be interested:

"In the PLC you can check with the lifebit from the areapointer coordination. It should toggle aprox. 1 time per second, but depending how busy is the panel it can also take 5 up to 10sec, cause the areapointer has a lower priority as normal tags or other jobs.

The lifebit is in the first word from it fro example Areapointer definition is DB1.DBW0, length 2 words then it is DB1.DBX1.2 An overview about the Bitorder in this areapointer is in the WinCC flexible Help. Search Index for Area Pointer and then coordination."