On Jan 30, 2011, at 2:25 PM, Tim Mitchell wrote:
> Some chips work above their rated max frequency, some don't. I had a batch of AT90USB1287 chips which are only supposed to work up to 8MHz at 3.3V, about 95% of them would run fine at 16Mhz. I found this out by accident, I hadn't read about the 8MHz limitation in the datasheet...
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> If this is a one-off device and you have a chip that runs at 16Mhz, you'll be fine. I would not do it for production though as sooner or later you will get some that don't work.
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I'd avoid doing it at all if possible. It might work today, it might work tomorrow but it might not the next day. Temperature is one variable that might affect it's working, if it gets too hot or too cold it might stop working. Also it might work, or at least seem to but you might be getting errors that throw off the circuit's operation without causing it to fail altogether.
If you are going to do it then I'd up the frequency till it stops working and then back it down well below that. If you want to run it at 16 MHz for example and it breaks at 17 MHz then I wouldn't trust it at 16 MHz. If it got up to 20 MHz before it failed then 16 MHz MIGHT work okay.
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Clark Martin
Redwood City, CA, USA
Macintosh / Internet Consulting
"I'm a designated driver on the Information Super Highway"
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