S7 312c

Hi
S7 312C PLC with a MMC card installed crashed, SF led on, PLC stop.This was caused by a program error, transfering to a DB not called. I tried a warm restart but the PLC stayed in stop mode. How do you reset the CPU so the PLC can run again? Also do you have to call a DB (as you do in S5)before you move data to a DB?

Appreciate any info.

Homer

Put some safety C DB?? command to OB1, or check thruth whole program if C DB missing before dataword/byte/bit etc. handling.
Download that routine and try reset and start by developper (see Mylo's post).

Usually when nesting, there have to be open db in the nested subroutine or in the routine who is calling (nesting) that routine or in routine who calling routine who is calling etc.
So. DB must be opened before calling or before datahandling.
If there are C DB command in nested routine and C DB command before calling in upper routine, system stacker return original DB open, who was open before calling in the upper routine.

Don't believe you have to CALL a DB for it to work, Have you defined data types correctly (Matched).
Try a MRES to restart Cpu.[Cpu in stop state with programming device or by means of the Cpu selector switch(hold switch in position MRES at least 3 secs, release, and then, after a maximum of 3 secs, hold switch again in position MRES for at least 3 secs] for a memory reset..........

As mylo stated you do not have to call a DB for it to work, like you did in S5, providing the DB being written to is set up correctly for what you want to write to it then it will work just fine.

Going on the little information that you have given us, I would check that firstly the DB has been downloaded to the CPU, and secondly the DB data areas have been set up correctly, i.e you are not trying to write to a data area that has not been declared.

Paul

Further to my previous answer, below is a mistake that I sometimes make (usually when debugging and editing after the initial download).

You will see that in OB1 I have used SFC20 (BLK_MOV) to transfer 9 bytes of data from OB1's local memory, starting at byte 20, the destination for this data is DB1 starting at byte 0, but if you then take a look at DB1 you will see that it is only set up to receive 8 bytes of data, not 9, this will then cause the CPU to fault.

I am not saying that this is your exact problem, but I decided to post this so that others may see the mistakes that are very easy to make, this is especially so when dealing with large chunks of data unlike the example I posted.

Paul

Seppo, Mylo, P Lucas,
Many thanks for your replies and information. I am sure I now know what is wrong although I am not sure how to fix this problem. As I said in my first posting we have a S7-312-C PLC with a MMC card fitted.The program I down loaded to the PLC require access to a DB but I did not include a DB in the project ie DB called by program - no db found - hence PLC stopped. The problem is the program is on the MMC card, because the DB is called almost immediately,the PLC goes into stop mod, I have no input I can switch on/off to interrupt this.If I remove the MMC card I can reset the PLC, but cannot down load program to PLC as I get bottleneck/lack of memory messages preventing this.
My question is how can I delete the program on the MMC card when I cannot go Online with the PG because the PLC goes into stop mode with "SF led on" whenever I insert the MMC card into the PLC.

Hope this is enough info.

Thanks Homer

Hello Homer;
First, if your CPu is in Stop mode (even with the SF LED active), nothing stops you from downloading a corrected version of the progamm, then switching to Run mode (key switch or Step 7 PLC/Mode function); if your new version has no defects, the PLC should come up correctly.
Secondly, how do you know that the problem is linked to a missing DB? I presume you have used the Module Information/Diagnostic buffer to obtain information on the problem. Normally, if you have a missing DB, the Diagnostics buffer will ask you to insert a diagnostic OB function to help correct the problem, for example OB122. In the Step 7 Blocks folder of your program, right-click the blocks window, Insert a new block, Organisation Block, create an empty OB122 (if that is the required number) and download it to the CPU. This should allow you to remain in Run even if the SF LED is still active, and increase the amount of diagnostics avilable in the Diagnostic Buffer.
Hope this helps,
Daniel Chartier

Hi Daniel
Thanks for the reply. DOH! I did not try and down load the revised program as I, (studiply) thought you could only do this with the PLC in RUN mode. The PLC is now up and running OK. Thanks for pointing out the obvious!

Homer

Up to speed

Hi Rack,

You are experiencing many problems that I have faced for some time now that I find can be coached via the telephony. You sound as if PLC's are fairly new to your environment and in it's infancy, you could maybe benefit from our company. I see you are UK based.

We offer 24hr telephone back up and site/home attendance if required with pre-agreed timescales.

Enjoy picking up Siemens, it's worth the effort and maybe you or a decision making supervisor would be interested in the safety net of this support until you feel more conversant.

Omelettes are only made by breaking a few eggs so give it a go.

Maybe we'll bump into each other here another time.

PLCN

wow! This is an old post

PLCNurse

Welcome to the forum! :site:

originally posted by PLCNurse
You sound as if PLC's are fairly new to your environment and in it's infancy

Click to expand...

As this post is one year old, I think that your statement might not apply to Rack Failure anymore

Paul

Kind of makes you wonder what PLCNurse's 'pre-agreed schedules' might run to!

Any way, is this touting for business? And if so, isn't it against the spirit of the forum?

Regards

Ken