Hang up on pic17c756 with external bus

Hi, I have finished an equipment with a pic17c756 working in extended mode (microprosesor and microntroller). My problem is when i plug / unplug the transformer my equipment hang up.
I conected it to battery and disconnet transformer from board and when i plug /unplug from line the equipment hang up.

Well this toldme that some electromagnetic flow hang my board.
I download the cristal from 16Mhz(bus 4Mhz) to 4Mhz (bus 1Mhz). And still hang on.

I dont know what i could do, to solve this problem.
I tell to my boss to shield the transformer but this is not cheap

If any have some advise or were i could read about how to desing microprocesor bus.

Thanks in advance

juan_manuell,

is your watchdog and brownout detect enabled?

Do you have external inputs which are directly connected to the processor and are connected to you board via wires?

I would suspect that you are catching some spikes via your inputs or supply.

Check decoupling of inputs and supply.

best regards

Hi C-Man

C-Man said:

is your watchdog and brownout detect enabled?

Click to expand...

Yes both are enabled

C-Man said:

Do you have external inputs which are directly connected to the processor and are connected to you board via wires?

Click to expand...

No, some sensor past trought opto´s and my keyboard pass throght encoder

C-Man said:

I would suspect that you are catching some spikes via your inputs or supply.

Click to expand...

I was thinking on bus in that case, and in all supply i put 0.1 uF to decoupling

C-Man said:

Check decoupling of inputs and supply.

Click to expand...

Could you recomend me some methods

Thanks for your help

If the watchdog is enabled and your program is still hanging I would carefully inspect where the watchdog is reset in your program.

You should do this only in a few routines, if you reset the watchdog too often you might be hanging for example in a loop where the watchdog gets reset but your program hangs there.

I once had a situation with a dataflash from Atmel where SPI communication did hang when a relais (which switched a motor) was switched on. Carefully selecting where the watchdog gets reset could at least trap this situation.

Not very easy to give you a good advice here, too many variables ...

Maybe you can try to connect no or as few as possible external sensors to your board and check if this makes a difference.

Also check if you have any unconnected (floating) pins on your processor they can do a low of harm in EMI situations.

best regards

Hi

C-Man said:

If the watchdog is enabled and your program is still hanging I would carefully inspect where the watchdog is reset in your program.

Click to expand...

Sorry, i forget to tell that when started to hang i enable the WDT and make some checks and the soft restart. But the problem is that this condittion it is not acepted

I leave from the board the external ram, RTC on I2C bus.

The problem is that graphical display 240*64 hang too and micro still running. unique solution turn on device.

C-Man said:

Not very easy to give you a good advice here, too many variables ...

Click to expand...

I know, thanks in advance for you help

C-Man said:

Also check if you have any unconnected (floating) pins on your processor they can do a low of harm in EMI situations.

best regards

Click to expand...

Ohh.. I forget that i have someones floating and 2 are a/d inputs.
Maybe this could be.

Thanks again

Hi to all,
The solution for the noise was, put a piece of copper to shield the copper layer were is the bus of microontroller. And this result the best solution