Are Pic pins normally LOW when the PIC is un-powered??

[Archangel]

Sounds like it is "Back Feeding" power into the PIC. Backfeeds can blow the PIC

[pedja089]

Hm, LED from PIC to +12V? Isn't that weird?
PIC operate at 5.5V maximum.

[Archangel]

With appropriate dropping resistor under load voltage will be correct, but when pic pin is hi Q . . .

[Heckler]

Yeah, I have the PIC running off of 5V for Vdd.
I did the calculation for the LED current limit resistor to take into account the 12V (using a 2700 ohm resistor) for approx 5ma LED current.

I thought the PIC could just be a source of Gnd (LOW) when I wanted to turn the LED on.

I had assumed that the port pins would be in a High Impedance state when powered down, and until configured otherwise.
Guess I'll have to insert a transistor in the ckt to control the LED.

Anybody else had any experience with how the I/O pins behave when the PIC is powered down??

thanks

[Heckler]

Now that I think about it...

Even if the pins were high impedance while powered down, the way I had wanted to supply ground (LOW) to light the LED would not have worked because when I wanted to turn the LED off, by making the pin HIGH, that HIGH (5 V) would still have been lower (with respect to the +12V) and so the LED would have seen +7v across it.

Back to the drawing board

[amgen]

With pic powered down, I don't think you can supply voltage/current to most all pins. The limit diodes direct the current back to Vdd powering up the device and probably not run the program properly.... per Archangle.
don

[falingtrea]

Most pins on a PIC can drive hi efficiency LEDs directly. Either connect the LED to 5V instead of 12V, or flip the LED and connect it to ground. Size the resistor for 3-5 mA of current at 5V.