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what happens if pic fails to start?

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Sajjadkhan

Sajjadkhan

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I want to know if PIC fails to start then what voltage will be on its pins. i have connected 2 pins of pic to LM317 with external transistors for battery charging.
when
pin1=1 and pin 2 =0 then, voltage =14.4V
pin1=0 and pin 2 =1 then, voltage =13.8v
pin1=0 and pin 2 =0 then, voltage =30v and a current limiter limits the current and acts as a constant current source. but this stage is not for too long else battery will damage.

so if pic fails and there is 5 v on any pin then i am safe but if 0v appears then puffffff.
 

Sounds dangerous. I don't know what happens if it fails to start, but if the PIC loses it's supply voltage, all pins will be low.

If you use 3 pins, you can make it stupid-proof:
pin1 high => voltage =14.4V
pin2 high => voltage =13.8v
pin3 high => voltage =30v
Override: two or more pins high => charger = off
 

You could put pull ups on the transistor bases so by default they are off. (If you haven't done already)
The micro's outputs should not drive low if the pic fails to start.
They are configured as inputs on reset, so should be pulled high by the pull ups.
 

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