AVR-Chat

So, what if GND as well as Vcc to the chip are both turned off, i.e., all uC
power pins are isolated, but now from some other source a voltage is applied
to an I/O pin (but is floating with respect to the uC)?  Would that in and
of itself be better than if GND were still connected?  Steve

 

From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of John Samperi
Sent: Thursday, August 23, 2012 2:30 PM
To: AVR-Chat@yahoogroups.com
Subject: Re: [AVR-Chat] voltage on an AVR pin when powered off

 

  

At 06:21 AM 24/08/2012, you wrote:
>So what happens if there is no Vcc, i.e., there is no supply power 
>applied to the AVR,
>but at the same time there happens to be Vcc on, say, a digital 
>input pin or a UART RX line?

The chip will try and draw power from that line. It's VCC (and the 
boards' VCC) will be the
voltage present at the pin less 0.5V.

So it is never a good idea to have power on pins of a chip which is off.

Regards

John Samperi

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