In SX Microcontrollers, SX/B Compiler and SX-Key Tool, danh wrote:

Hi all, first post here.  I've had a problem lately where I've fried a couple SX28's so I'm here to ask for all your help.

I'm using RA0-3 as input pins reading the state of a 4-pin BCD rotary switch.  The data sheet for the switch is here, if you're at all interested:
[url]http://rocky.digikey.com/WebLib/C%26K%20Components/Web%20Data/CRD%20Series.pdf[/url]

I soldered the two "C" common pins to ground, and I've got the other 4 pins connected to port A pins 0-3.  I've configured port A as input pins, and enabled the internal port A pullup resistors.

When I run my code, everything seems to be working fine.  I can cycle through the switch settings and I see the values reflected on the input pins when debugging.  The problem seems to occur after a longer period of time, say greater then 4 hours.  I return to my circuit to find the SX28 now has a nice little brown color in its mid section and a nice crack at pin 7 (same for both failures) which is RA1.

Basically it appears that at some point, a short occurs on RA1 (pin 7) and really heats up the chip.  For all I know, it could be another pin, but the crack right at that same point both times seems suspicious.  Is there any way the internal pullup resistors could somehow get disabled while the code is running?  I'm going to try disabling the internal pull ups and using external ones.  Are there any "gotcha's" to watch out for when using the internal pullups?  

As far as I can tell, there's no short in my soldering/wiring, which is also backed up by the fact that the failure doesn't occur right away.  Also, I'm pretty sure that the switch circuit shorts at some point, because when I leave the switch setting at '0' (no connections) the failure never occurs.

By the way, I'm also using Port B to control an LCD and RC.7 to control a Relay.

Thanks for any tips and help you can offer!  Let me know if you need more info...

-Dan

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