Mega 8 fuses changing back to defaults

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We are getting ready to put a device with a mega 8 into production. A batch file is used to program the device and set the fuses for the 8 MHz internal RC oscillator. A few of the devices are not working right because they are set for 1 MHz. The problem is worse than it sounds because after the units are potted, the fuses can not be reprogrammed.

The story is that the batch file can only set it for 8 MHz and these units somehow changed back to 1 MHz. Has anyone had experiance with that?

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Not with fuses "changing back". What I'd suspect is that the fuse setting to 8MHz isn't "taking" for some reason--too fast ISP; too soon after previous operation and the chip is still "busy--something like that.

If your "production" is decent quantities, investigate having your distributor pre-program them. If moderate quantities and you want to continue programming them on your production line, I'd implement more readback steps, make sure the verify is used, make sure error checking is proper, and similar.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Once the clock fuses are programmed they stay at the setting EVEN THROUGH CHIP ERASE. So they aren't "changing back" they are not being set in the first instance! You have a prob in your programming timing etc as mentioned by theusch

There are only 10 types of people in this world ; those that understand BINARY and those that DON'T!!!!!!!