Reset problem

[leonel]

Hi...
Sorry to be out so long!
I'm facing a big problem with reset condition on PIC16F57, this is, when i turn on a motor by a relay sometimes my microcontroller makes a reset. I faced the same problem in PIC16F872 and i solved with a 4,7uF capacitor in MCLR pin, but in PIC16F57 doens't work.
Does anybody had this kind of problem?
What i have to do?

[DynamoBen]

Try putting a .01uF cap near the PIC between Vdd and Vss. You also may want to try a 10uF cap at the output of your voltage regulator.

Do you have a diode between the relay coil contacts?

If none of these suggestions work a schematic is going to be nesscary.

[modifyit]

If you can, check the STATUS register after the reset occurs and see if it tells you why the processor reset. It may be caused by power flucuations when the relay turns on the motor, and not by the mclr pin at all.

[mischl]

you are really sure that is a reset and not a undebounced input which executes an unexpected part of the code?
how is the BROWN-OUT RESET configure?

good luck

[leonel]

Well, i think i solve my problem.
I have a 78L05 well regulated output with a 10nF ceramic capacitor between +5V and GND, also i also have flyback diodes across inductive loads.
What i did was to increase a little bit my MCLR pin with a diode. (likely the cause was the MCLR pin voltage decrease a little bit), I saw in datasheet and Voltage on MCLR with respect to VSS can go to +13.5V. Also, put a 10nF cap between Vss and GND (near my PIC).

[sayzer]

Here is something to add as a solution for those who still have reset problems.

1: Use 47K trimpot on MCLR pin.
2: Adjust the trimpot untill the resetting stops. Requires hard reset after each change.
3: Remove the trimpot, measure the resistance value, and use a resistor at the same value.
4: Done.

BOD_OFF did not work for me but a trimpot at MCLR pin solved the problem.

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