Hello,

I'm looking for some help with an S7-1200 PLC (121C CPU).

I have it as the main PLC working properly with an already implemented program (TIA portal). Now I have added a reset button to an HMI and I have it linked to a tag. But I don't know how to implement a reset. Is there a function that can interrupt the current running of the program and perform a reset (set all values to default, clear buffers, start the probram etc.)? If so can you please let me know what function it is and how to use it? Thanks in advance

Hello dantes1111,

the following links might be of interest for you:

Reset CPU and DB

Initialisation of DB by using the SFC83

regards

eisenpferdreiter

Hello dantes1111,

the following links might be of interest for you:

Reset CPU and DB

Initialisation of DB by using the SFC83

 

regards

..for the S7-1200 ( CPU1211C )?

One thing you could try:

configure the "startup after POWER ON" setting of the CPU to "Warm restart - RUN". This configuration item appears under the "Device configuration" for the CPU under "Startup".

Then with your tag set a binary output, where you trigger a hardware-monoflop (timer relais), which interrupts power from your CPU for some time (for example 500ms). When power is back, the CPU will perform then a sequence of power-up diagnostic checks and system initialization. During system initialization the CPU deletes all non-retentive bit memory and resets all non-retentive DB contents to the initial values from load memory and then enters the appropriate operating mode.

regards

dantes1111

Hello,

I'm looking for some help with an S7-1200 PLC (121C CPU).

I have it as the main PLC working properly with an already implemented program (TIA portal). Now I have added a reset button to an HMI and I have it linked to a tag. But I don't know how to implement a reset. Is there a function that can interrupt the current running of the program and perform a reset (set all values to default, clear buffers, start the probram etc.)? If so can you please let me know what function it is and how to use it? Thanks in advance

Hi.

From the description it seems as though you are used to designing for micro-controller circuits. Those normally have reset buttons for such purpose. ..I do not know your background in PLC design please correct my assumptions.

PLC systems cycles/scans through the entire program. There is no PAUSE or WAIT or any such commands that will make the program get stuck on a set line of code that might need a reset. Even if you have a badly designed LOOP the Watchdog Timer will place the PLC in STOP.

Maybe you know all this.. maybe you do not. The guys will be happy to guide you in a more detailed explanation, if needed.

If your intend is to initialise memory positions with default value - then you have to write some code for that.

Please guide us with more detail and then we might be more zoomed in on your question (if we have not done so already).

Regards,
w

Hello Everyone,

Thanks a lot for your help.

So to give you a bit more details, this is my first PLC program so definetely I'm a new at this. I read a lot of documentation before doing it and have now three systems with a similar setup using the 1211C as the main PLC. The purpose of this reset is to allow the operator/user to put the system into the default (initial) state directly from the HMI without having to manipulate any switches or power off/on. This might be required even when the process is running in a normal way.

Now I understand that the problem is I didn't do an Initialization function since the beginning, so currently once the PLC is powered on it just starts the program execution and to return to the initial state is to basicaly perform a RUN->STOP->RUN which can only be done from the programming interface (TIA) or by power off/on.

So the correct way to implement a reset would be to have an Init function where the initial conditions are setup and a bit is set once the systems is in the initial condition. Then have this initial condition bit checked at every step of the program and then use the HMI to set the tag that would put the system into this initial condition... So should have done that when started not after the program is written;)

Anyway I will have to eventually do this, but for the moment I found a posibility to do the RUN->STOP->RUN from the HMI, I have a KTP600 and there is an insturction SetPLCMode which can be used in the events of a button for example and this instruction can set the PLC either in STOP mode or in RUN mode. I guess this solution is not a good one (will stop the program execution) for the long term but maybe can help while the right approach is implemented.  

I can see that you have put good thought into this.. good!

You can develop initializing routine within OB100 for STOP >> RUN or at least activating condition markers that activate some action.

I however see no reason for you to force the PLC to go through a STOP >> RUN transition. You may have unintended functionality that you cause because of this. Also.. the S7-1200 has the ability to store some of the conditions even through a STOP >> RUN.

Rather go the "control freak" route: adapt and add coding to bring the system to a state that is under your program's control. Regardless if it is a human selected action or STOP >> RUN.

Please put some more thought in this to NOT force STOP >> RUN but rather a programmed response.

Good luck.
w