There are small RTU's of S7-300 comprising of 1 CPU 315-2DP, 1 DI, 1 DO and 1 AI card. They are connected via the U-Channel back connectors.

What level of diagnosis can I read from this system? As if I plugout a card, the PLC goes to stop and the data update stops. And if I can read it then how do I programme it??

 

Hi,
Siemens have many OB's that handle faults etc. Use the help file to see what ones you require. If you put an OB in the program it will stop the PLC from halting even if you don't have any code in it, i.e. OB122 will be called on module fault. You can put your on code in the OB to intergate what called the block or write what ever code you want.

Kevin

 

Hello Saad;

SiemensS7 CPUs offer a very powerful diagnostic tool that operates in conjunction with the diagnostic OBs pointed out by Kevin.
It is called the diagnostic buffer. One of the ways to access it is to go Online while you are in the HWConfig editor. The online view will show the status of all modules in the project, including Profibus-DP slaves, with red crosses showing defective units. Double-clicking on any of those will bring up the diagnostic buffer of that module; the CPU's is of course the most informative.

Some of the entries in the diagnostic buffer will state "Missing or required OB" followed by an OB number. You must then create the required OBxx (in the blocks folder) and download it to the CPU (even with no programming inside the OB). This will stop the CPU going to Stop mode when the particular error the OBxx was designed for appears, and will help the diagnostic buffer collect data on the present fault.

Look up "diagnostic buffer" and "diagnostic OBs" in the online help of Step 7 for more details.

Hope this helps,
Daniel Chartier