How to restart S7-300 on fault

Is there any way to restart CPU after runtime error has occured?

We have a program with quite a lot of overflow bugs that we are currently fixing. Those bugs occur after certain amount of days. I've thought of quick and temporary fix by restarting CPU.

There are OB121 block that executes if any error happened. Now I need some king of STL intruction to restart the CPU from within this block.

If OB121 exists in the plc, the CPU will not stop - it will execute the code inside the OB and then continue from where the error occurred.

Hardware Solution

I believe there is no such thing as an automatic restart done by software.

but you can make it by hardware.

if the program runs OB121, you can set a bit, which change a relay at the power supply. the relay change the power supply (1 -->0) so the cpu doesn't have any power. if the PLC turned down, the bit changes (1 --> 0) according to power loss, and then the PLC is starting again, and starts OB100.

the only thing you need is a relay before your power supply

Kind Regards

I think that is bad practice.. And it sounds very glitchy..

There is a problem causing your cpu to stop, find the problem and fix it, that is the only viable solution. Using OB121 should keep your cpu running, but you still have to find the problem.