Re: 6502/6510 ROM selection daughterboard

From: Gábor Lénárt <>
Date: Fri, 8 Jun 2012 10:52:50 +0200
Message-ID: <>
On Thu, Jun 07, 2012 at 09:22:51PM +0300, Pasi 'Albert' Ojala wrote:
> On 06/07/12 16:41, Gábor Lénárt wrote:
> >resistor). In forums people say it's called "parasite power" that
> >it can work even without Vcc connected, if the MCU can get power
> >from other pins. However it sounds very strange for me, and
> >honestly I can't understand this.
> There are protection/clamp diodes from each input/output pin to gnd
> and to vdd. If the voltage in the IO pin is above VDD+threshold
> (0.6V), the diode starts to divert the current to protect the pin.
> So, you can power a chip from its input pins, although it is not
> recommended and not good for the chip.

Ahha, thanks for the information! After I programmed FUSE bits in ATmega8A
for Brown-Out-Detection, then this does not happen.

Anyway, the lesson (for me at least): just not powering a chip, does not
mean that you disabled it :)

       Message was sent through the cbm-hackers mailing list
Received on 2012-06-08 09:00:05

Archive generated by hypermail 2.2.0.