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Using a V570 with a e3xb snap in module. App runs fine for awhile then crashes. Screen reads as follows:

stop mode fatal error


ip:0x0035729A 00348f6a


desc. watchdog

I've tried a different 570 and a different snap in but problem pops back up. I get no errors when compiling. I don't believe it's a wiring issue but perhaps. Any insight would be greatly appreciated.



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Hi Matt,

I'd have to say that is the dreaded screen that can sometimes be a mission to resolve :(

Firstly, have you checked your program for any possible "Loops" where the Program Scan would take too long or wouldn't end? If you want to upload your program or send it to ash@comtech.co.nz I can inspect it for you.

Secondly, I have found that tiny shorts in electrical wiring can actually cause the PLC to "Semi-Halt" for a few Milliseconds which causes the Watchdog Error Screen to come up. In one installation, it took us about 3 hours or testing, jiggling and wiring before we found a Pressure Transducer that had two wires shorting every now and then.

Lastly - This could also be caused by EMI (Electro-Magnetic Interference), which can be produced by anything AC based that is switching a big load or varying switching frequency - like a BIG solenoid being switched on and off or a VSD (Variable Speed Drive). You can actually buy meters that will tell you the level of EMI around them, but the easiest step is just to check if you do have any of these EMI producing devices.

Have a look at the above things and get back to me. Hopefully it's an easy fix once I have some more information :)

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High probability that the PLC is locking up from inductive transients - I've experienced this. Do you have RC snubbers or flyback diodes on all your inductive loads? The reverse EMF that is caused by something as small as two plug-in octal relays releasing at the same time can find its way into the I/O module through the board traces can cause this kind of hiccup.

Joe T.

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Hi Matt,

In general these kind of errors are generated by watchdog timer in case the controller exceeds some predefined time and didn't pass trough Scan end. The reason can be too long code, internal loop, logical error.

In some cases, it can be related to external events, like switching contactors, solenoid valves and power relays, motors and motor drivers, welding works around…

Does it happen on specific action or randomly? Can you simulate this error?

Does the same error occurs when the V570 is on your desk?

Where the PLC located? What is the environment?

Please check the following:

Calling to displays and alarms displays are with one shot condition only.

Calling a label and creating internal loop

Calling to subroutines in a way that you create loop between subroutines and never go back to main routine.

Make sure that you are using the latest VisiLogic version 8.6.3 and OS version 3.1(30).

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