16f1824 MCLR pin going low causes PIC to reset - what am I missing?

[HankMcSpank]

So I want to use pin 4 (RA3) as a switch input pin, I've enabled weak pullups...I measure 5V on there - all seems as it should, but whenever I press a switch (which ground the pin), the PIC resets (I have an Hserout command at the top of my code, so I see the word "reset" only if erhm,....the PIC has reset!)

So I have this as the config.....

@ __CONFIG _CONFIG1, _FCMEN_OFF & _FOSC_INTOSC & _WDTE_OFF & _MCLRE_OFF & _CP_ON & _IESO_OFF & _BOREN_OFF & _PWRTE_OFF
@ __CONFIG _CONFIG2, _PLLEN_OFF & _STVREN_OFF

I thought the bolded entry allowed me to use pin 4 (RA3) as a normal digital input.

Is there anything else I have to do to stop the PIC barfing just for grounding the MCLR pin?

[ronjodu]

That pic is new to me but it looks like you may also need to check the configuration word 1 bit 6.

[rsocor01]

Are you using an external pullup resistor for your switch configuration?

[HankMcSpank]

Are you using an external pullup resistor for your switch configuration?

no...if i'm reading the datasheet correctly, it is possible to use a weak pullup for that pin, which is what i've done...

OPTION_REG.7 = 0
WPUA =  %00011000
IOCAN = %00011000

[rsocor01]

no...if i'm reading the datasheet correctly, it is possible to use a weak pullup for that pin, which is what i've done...

Hmmm, try using an external resistor (maybe 4.7K Ohms) and see if you have the same problem. You might be drawing too much current when closing the switch and that might be causing the problem.

[HankMcSpank]

just tried an external pullup resistor on RA3 (vs internal weak pullup)- same results.....if I ground RA3 (MCLR pin), the PIC resets

...aaaaaaarrrrgggHHHH