APM1.4 2560 failed I2C

Hi,

Just before maiden of my Funjet APM stopped working. After few hours of debugging I figured out I2C devices are not working, preventing APM to initialise. After all I wrote simple program

void loop() {
  digitalWrite(20, HIGH);   // set the LED on
  digitalWrite(21, HIGH);   // set the LED on
  digitalWrite(15, HIGH);   // set the LED on
  digitalWrite(14, HIGH);   // set the LED on

 delayMicroseconds(5);
  digitalWrite(20, LOW);    // set the LED off
  digitalWrite(21, LOW);    // set the LED off
  digitalWrite(15, LOW);    // set the LED off
  digitalWrite(14, LOW);    // set the LED off

  delayMicroseconds(5);
}

After executing an all pins except SCK there were nice rectangles. SCK seems to be crippled as seen in attachment. This was measured without Oilpan.

Please confirm that my only chance is to replace Atmega. Replacing won't be issue, but I hate to order it.

I still trying to figure out what can be cause. My first idea was static discharge as i was wearing fleece jacket. But I've been said that most modern parts should not be destroyed by ESD. Another possible but very very unlike is short of SCK pin to +lipo.

Tags: ESD, I2C, discharge, static

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Permalink Reply by Jake Stew on April 4, 2012 at 2:54pm

>  most modern parts should not be destroyed by ESD.


Most parts have actually gotten more and more susceptible to ESD.  The smaller, thinner and more complicated they make the part the more easily it is destroyed by ESD.  Because of this some parts have additional ESD protection built into them.


ESD can cause intermittent failures, partial damage, or otherwise be hard to spot during testing, that's what makes it such a PITA.

Permalink Reply by kolin on April 5, 2012 at 12:23pm

It probably was static discharge. Luckily damage on my MCU is obvious, SKC pin have crippled output even with pin in air. But AVRs should withstand human body model testing as said in Atmel's note

Whole CPU seems to be working, except one pin, thats pitty

Permalink Reply by Jake Stew on April 5, 2012 at 1:15pm

The human body ESD model is just a formula for testing that gives you a number to put in your datasheet.  It in no way means it can handle a static discharge from touching the component.

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