Tuesday, November 16, 2010

How to rescue AVRs with wrong fuse bits

It can really be hard to rescue AVRs with wrong fuse settings without a HV-programmer.
But there are a few ways to do it.
In todays blog, I'll show a few of them to you.

The first thing to try out is providing an external clock at the XTAL1-pin.
The clock frequency has to be higher than one kilohertz and lower than something about 16 Megahertz.
This is a rather big frequency spectrum, so there are many possibilities getting such.
Anything from the simply NE555 oscillator with only two external parts over the calibration clock of a oscilloscope to a crystal oscillator will do the job.
Try to implement a pin-like place to apply it on your board if you design a PCB.
It helps.

Still not running?
So try out the second option: Get out your old parallel programmer and connect VCC, GND, RESET, MISO, MOSI, SCK and XTAL1.
The programmer will deliver a clock perfect optimized on the programming speed.
Try also slow-ISP or slightly higher voltages.

If nothing has worked yet, solder wires to all pins and build up a high-voltage programmer (if you don't already have one) like the AVRdoper (http://www.obdev.at/products/vusb/avrdoper.html).

Hope your controller works now!

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