How to recover from AVR chip deadlock caused by wrong fuse position

When you change the fuse configuration of the AVR and re-power on, and then try to use ISP to download, the prompt "Failed to enter programming mode" appears, etc. It is very likely that you have made a mistake in the fuse settings, causing the chip to not know which main frequency to use and unable to work properly (only limited to the case of internal RC oscillation).

The solution is:

1. Send it back to the chip service provider and ask them to help restore the chip

This is the easiest, but most time-consuming and most helpless method.

2. Use the programmer to restore the chip to factory settings

This method requires you to have a programmer. For detailed information on how to make a programmer, please refer to the post on the technical forum of this website: Using 89S51 to make a simple parallel programmer ATmega16 (Resurrecting ATmega16).

Supplement: On October 27, 2004, Rainbow Digital, a member of this website, provided a method to restore the chip by changing the fuse position in the Weihuang series programmer. For details, please go to the postscript and supplement at the end of this article.

3. Restore it by adding an external active crystal oscillator.

This method is the most feasible. It can recover most chips with wrong fuse positions. The connection method is as follows:

Recovery method:

Connect the active crystal oscillator shown in the figure above, re-power it on, and then use the ISP download cable to modify the wrong fuse position. After the modification is completed, turn off the power, remove the active crystal oscillator, and see if it has returned to normal.

There is another way. If there is no active crystal oscillator, you can use the clock of other working microcontrollers as an external crystal oscillator. Just connect the XTAL2 pin of the working microcontroller to the XTAL1 pin of the microcontroller with the wrong fuse setting. For example, if I use the AVR910 download cable, I can directly connect the clock output of AT90S2313 to the wrongly set chip to restore it. It is very convenient. (This method is provided by Rainbow Digital).

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Postscript and Supplement (2004-10-27): Rainbow Digital, a member of this website, provides a method to restore the chip by changing the fuse position in the Weihuang series programmer.

As more and more chips are locked these days, there are no more chips available, so I have to take out the Weihuang 500A parallel programmer I bought before to study it. Because I have never found that the programmer has the option of changing the AVR configuration fuse (as shown below), I didn't have much hope.

After selecting the M16 chip in the 500A burning program, a dialog box popped up. In the past, I always looked at how to connect the AVR-2 adapter, and never paid attention to the words in the red box in the picture below.

After careful reading, I suddenly remembered that the configuration fuse interface in SLISP also has high and low byte bits, so I quickly opened it to have a look. Sure enough, the high and low bits and the extended bits correspond to fuses with different functions, as shown in the following figure:

Finally, I understand that the so-called fuse is actually a 3-byte memory. Different values ​​represent different function settings. Therefore, the Weihuang series programmer only needs to manually modify the fuse address (the fuse address of different chips will be different) in the data buffer and then write it, as shown below:

For a detailed discussion, please refer to the forum post on this website: New Discovery: The True Face of Fuse and How to Change Fuse with Weihuang Series Programmer

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Appendix 1: Brief information: Crystal, crystal oscillator and active crystal oscillator

A crystal is a piece of crystal (natural or artificial quartz) cut in a specific way (such as AT or BT), and the piezoelectric effect of the crystal is used as a frequency reference.

Add an oscillation circuit (such as Kleipzig, Colpitts, etc.) to complete a complete circuit function, and then package it, we call it an active crystal oscillator. Relatively speaking, a crystal without a circuit is called a passive crystal or a passive crystal oscillator.

Appendix 2: Fuse bit reference diagram for Mega8 chip using SL_ISP 1.3

8M internal RC oscillator

1M internal RC oscillator