>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>Sent: 08 September 2005 04:11
>To: Microcontroller discussion list - Public.
>Subject: Re: [AVR] Brown out problems
>
>
>> Has anyone seen problems like this before?  Is the Mega128 internal
>> BOD not capable of handling slow voltage rises?
>
>I've seen it on other processors.
>About nothing built can handle reaaaaaally slow rise times. Some 
>manufacturers give a rise time spec (eg Philips), some don't (eg Zilog 
>(in cases I am aware of). In the latter type of cases you can claim 
>failure to meet published specs, but don't expect that to help.
>
>If you have really slow rise times the only guaranteed way to fix 
>things is to control the power supply turn on. Effectively provide a 
>brown out detector on the power supply and never apply power to the IC 
>until you can turn it up at a guaranteed OK rate. Sounds drastic but 
>anything less can cause problems. Ask me how I know ;-) .

Thank Russell.  Unfortunately prototypes are built have have to be shipped to customer shortly.  This may or may not be a problem in service, I only noticed because the Thurlby PSU's we have in the lab are notorious for creating death inducing transients when the output on/off switch is used, so we simply wind the current control up and down to turn the outputs on and off.  In ~6 years of 16C, 16F and 18F PIC based products we have never seen a brown out issue from this.  This is our first (and probably last) AVR based one....

The EEPROM corruption is a worry, but possibly workaroundable, what concerns me is the spurious garbage I get out of the serial link until the watchdog timer kicks in.  I was wondering if the oscillator has not started up properly by the time the BOD has released the reset, giving some odd baud rate, but it does not explain why the watchdog reset occurs shortly after. The only logical explanation I can think of at the moment is the PC is wandering off in the weeds.  Unfortunately this is pretty difficult/impossible to catch with a debugger!

Regards

Mike

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