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PIC processor leeching power throug the A-port!

 
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davidbue
HG Junior


Joined: 06 Oct 2006
Posts: 12
Location: Denmark

PostPosted: Fri Jun 01, 2007 12:11 pm    Post subject: PIC processor leeching power throug the A-port! Reply with quote

Hi everybody.

Now here's a strange problem that I hope that one of you guys can help me with. I have done alot of PIC programming, but all subsytems of my earlier projects has been fed by the samme powersupply, and all my communication with the surroundings has been done through a Max232 chip, so I don't really know if this i a stupid question:

I communicate with a PIC18F2220 through the parallel port of a PC. Ground on the parallel port is connected to the ground plane of my PIC board. I use pins on the A-port of the PIC to recieve signal from the output pins on the parallel port. I run the pins of the parallel port directly into the PIC processor.

On my test-setup my PIC controller turns on LED's to indicate when pins on the parallel port is either high (3.3v) or low. This works fine.

Now to the problem:

When I set an output pin on the parallel port high, and turn off the lab supply powering the PIC board, the PIC controller continues to be live, and the LED (that shows that the parallel port pin is high) is still on.

This is what i find strange. No supply on the VDD/VSS pins, but the PIC lives on!

When i set the pin on the parallel port low, the LED goes out, and the PIC processor stop leeching power through its A-port and hereby stop running.

Is this behaviour expected?

If not, what am I doing wrong?
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BronzeG3
HG Master


Joined: 30 Apr 2006
Posts: 134

PostPosted: Fri Jun 01, 2007 4:21 pm    Post subject: Reply with quote

I've had the same thing happen with PIC's I've used. They will leach power from where ever they can. The only thing I can think of is to use opto-isolators between the PIC and PC.
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davidbue
HG Junior


Joined: 06 Oct 2006
Posts: 12
Location: Denmark

PostPosted: Fri Jun 01, 2007 5:16 pm    Post subject: Reply with quote

Hi BronzeG3

Thank yuu very much for the quick reply. It's nice to hear that I'm not the only one who have experienced this behaviour. I'll thow in an optocoupler to solve the problem.

Best regards
David
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