Message
Ground oscillations and flash on Mega16
2005-05-30 by Roy E. Burrage
1. Signature bytes could not be read
2. The oscillator quit, using external crystal
3. Fuse bits could be read but not written
4. Lock bits could be read but not written too
5. Further programming (serial ISP, HV serial, and parallel) is not possible without a failure indication
Has anyone else experienced a similar failure mode? It appears to have killed several controllers...D-E-D, dead.
Ground for the power amplifier is connected to the on-board digital and analog grounds, but only at a single point. A star ground scheme is being used with single point connection of the power, analog, and digital grounds. I wasn't able to see humongous chip killer spikes on the ground, but also didn't attempt to recreate these since it also seems to be killing the chips. Once the problem occurs the chip is not programmable either in circuit, in an STK500, or a Mikroelectronica development board.
All I/O pins are isolated from the world by at least a 10K resistor in series with the pins. Inputs are pulled up to +5 volts, grounded for input. All outputs that go to the power section are isolated by at least 10K in series with a buffer transistor or an op amp. The power section is still only 18 to 20 volts DC, but can provide as much as 15 amps...with only a 2.5 amp load during debug.
I've never seen a problem such as this but this is also the first Mega16 project of any complexity.
Any ideas?
TIA,
REB