PLC resets

[dan]

Hi,

I realize that this is software problem, but looks like I can't see the forest from the trees.

I have several "While" and "If" loops correlated whit communication with the COMM2. There is only one section of the program that I believe that resets the PLC (I'm loosing all data in variable and DM)
If I don't access that part of the programs (inputs are not activating  the custom function) everything is Ok.

What are the possible reasons (software only) for the PLC to reset?

Thank you,

Dan  

[dan]

Hi,

more questions.
1. does T100 have a "build in" WDogTimer?
2. if yes can it be turn off ?
3. aprox after how many loops (or milisec) the WDT resets the PLC

Thanks

Dan

[support]

what's your PLC model?

All M-series PLCs have built-in watchdog timers which will reset the PLC if the program is stucked in a GOTO loop for more than half a second. It cannot be disabled. If you have a T100MX a WDT reset would show up on the fourth status LED (this is not available on the MD). On the T100MD the STATUS(1) command will report if the PLC was reset by WDT.

The PLC is not reset by WDT if the program is stucked within a WHILE loop. Only an infinite goto loop without a chance for the CPU to clear the WDT would cause a WDT reset.

Another possibility is that some high energy switching noise could cause the CPU to skip a beat and end up in some wrong opcode which would result in a WDT reset.

You may also want to investigate if any load connected to the PLC's output could have cause a glitch and drive the PLC's power supply to below 9V briefly which would cause a power on reset. A diode and E-cap connected to the PLC's power input as shown in the installation guide would be able to take care of such a problem.

[dan]

Hi,

Yes. I have a couple of Goto.

This helps a lot.

Thank you,

Dan