Re: [avr-gcc-list] ATMEGA FRIED!!!! HELP!!!!!

[Joerg Wunsch]

As =?iso-8859-1?q?Shadab=20Ansari?= <address@hidden> wrote:

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>is this device this much delicate that an accidental short of pins
>for just a few seconds can destroy it?

Well, the ATmega128 has much increased driver capability, compared to
other AVRs.  E. g. on most AVRs, you can safely connect a LED directly
from a port's output to GND, and the output transistor will limit the
current to a value that will neither damage the AVR nor the LED.  On
the ATmega128, you cannot do this, you always need a resistor to limit
the current.

When you short an output to Vcc, things are worse.  You're already
outside the allowable limits for normal AVRs, and if you extrapolate
the curves for the IO pin source current in the ATmega128 datasheet
(figure 184 in my version), you'll end up with some 150 mA per pin
when shorted to Vcc = 5 V.  The maximal current per IO pin is given as
40 mA, so yes, IMHO you're already at a big risk here.  (This assumes
shorting against hard Vcc, not against an output pin that is at `high'
level.)

However, I'd normally expect single IO pins to be more at risk than
the entire chip.  Verify your assumptions again: measure the idle
power consumption, and compare it with the datasheet's value.  Make
sure your cabling to the programmer is OK, and try to chip erase in
order to clear any possible lock bits.  Use an oscilloscope to see if
the oscillator is actually running.

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-- 
J"org Wunsch                                           Unix support engineer
address@hidden        http://www.interface-systems.de/~j/