Hello All,

OB's 80, 82, 86, 122 my understanding are used to capture faults.  So with out these being in the project - any time a fault occurs it will stop the processor.  So Siemens tells me to add these to my project and I will not have to re-start my processor each time something is unplugged... Ok, great!

So now I'm being told that I should put something in there to capture want happened so that it can be diagnosed Ok, What do i put in there? I mean if I put a set coil I guess I'll know something happened.  And of course I can diagnose it with SIMATIC (getting better at that)  However, I guessing that there is more information which I should be grabbing even if I don't send it to the screen at least it would be in the application.

What do you put in your OB fault catchers? 

And then there OB100 Complete Restart not sure if I'd ever want this to happen... seems like a possible safety issue. how have you guys used this OB on past projects? 

Any how I looked though the forums there an interesting discussion on scan rates.. however I didn't find something on the basic usage of these blocks ... and the manual i have just briefly discuss what an OB is. or tells me that OB82 is for I/O faults...  I need an example or pointed towards some long buried post.

Thank You & Regards

hi,

i try to give you a small overview how it works. 

OB´s are the highest level blocks.

OB100 will be execute when the CPU starts, exactly one time. 

After that, the main-program will be executed in OB1, the cyclic execution-block.

If an error occurs the CPU tries to call an OB, depending on the error that occurs, e.g. OB121 for programming error. If this OB is not on CPU the CPU will go into Stop-Mode. 

you can also do an error-handling in those OB, e.g. in OB86 you can detect which DP-node is wrong, so you have to send an error message to you HMI. 

There are many other OB´s that are called in several cases and conditions of the CPU. S7-help contains information of every OB.

hope this helps,

regards,

Hi

OB100 You do init.

OB86 - for profibus-see code below (array is at BEGINNING of global db and beginning of ALARMS db)

it shows which node failed/recovered:

ADDITIONAL TEMP VARIABLES:

Slave_Address: DINT;

Slave_Error: Bool;

Slave_OK: Bool;

AR1_Backup: DInt;

NETWORK 1

      L     LD     8                    // Extract Slave Address
      L     DW#16#FF
      AD   
      T     #Slave_Address

      L     #OB86_EV_CLASS              // Check if slave developed a fault
      L     B#16#39
      ==I  
      =     #Slave_Error
      TAK                               // Check if slave Recovered from Fault
      L     B#16#38
      ==I  
      =     #Slave_OK

NETWORK 2

      TAR1  #AR1_Backup                 // Save AR1

      LAR1  #Slave_Address

      OPN   "GLOBAL"                    // Open Global Variables Data Block

      A     #Slave_Error                // Error - Clear Bit
      R     DBX [AR1,P#0.0]

      A     #Slave_OK                   // OK - Set Bit
      S     DBX [AR1,P#0.0]

      OPN   "ALARMS"                    // Open Alarms Data Block

      A     #Slave_Error                // Error - Set Alarm Bit
      S     DBX [AR1,P#0.0]

      A     #Slave_OK                   // OK - Reset Alarm Bit
      R     DBX [AR1,P#0.0]

      LAR1  #AR1_Backup                 // Restore AR1

END

Hello,

I'm working on my first S7-300 project and I have the same question about these OB's. My colleague adviced me, that there is enough just to put these empty OB's to my project and it'll prevent PLC from going to STOP mode.

Is it really enough to use empty OB's?

Hi, hdhosseini,

Thanks for Your reply.

If I understand correctly, theoretically I can put empty OB's to my project, but if the error occurs PLC won't go to STOP mode, but it will do nothing, because of empty OB. Am I right?

MnDgS

Hi, hdhosseini,

Thanks for Your reply.

If I understand correctly, theoretically I can put empty OB's to my project, but if the error occurs PLC won't go to STOP mode, but it will do nothing, because of empty OB. Am I right?

 You´re right. 

The PLC does not go into Stop because of the error. It goes into Stop because it want to call the the OB because of an error, and the OB is not loaded. 

This is what you can read in the diagnostic buffer.

regards,

New question published by s.vali is split to a separate thread with the subject SIMOCODE, not reading process data.

Best regards
Min_Moderator