AVR fuses woes ...

[dmcole]

Anybody here a Mac-o-phile and using AVRFuses (http://www.vonnieda.org/software/avrfuses)? I've killed one ATMega8515 and I since I have only one spare, I'd like to get this right.

All I'm trying to do is to use an 8MHz external crystal. In the current version of AVRFuses, there's no listing for an 8MHz crystal. There's listings for "Ext. RC Osc. 3.0 MHz - 8.0 MHz," with various startup times, and "Ext. RC Osc. 8.0 MHz - 12.0 MHz," with similar various startup times.

But those are *oscillators*, right? Not crystals. But even if that's right, should I pick the 3-8 or the 8-12? Default startup time is 6 CK + 12ms; should I use that?

Then there is a list of "Ext. Crystal/Resonator" for "Low Freq." "Medium Freq." or "High Freq." at various startup times, none of which are anything like 6 CK + 12ms. Is 8MHz low, medium or high?

Thoughts, comments, theories for this dunderhead would be appreciated.

Thanks so much.

\dmc

PS: Short of that, the AVRDude CL for changing from the default internal clock to an external crystal on an 8515 (and nothing else, right?) would be appreciated.

PPS: Lastly, assuming I set the fuses to "Ext. Clock; Start-up time: 6 CK + 64 ms" on the now-dead 8515, any thoughts on how to resurrect it?

[adafruit]

you want Ext Crystal, not RC osciallator

[Sorceress Sarah]

Just out of curiosity. . .

What's this bug supposed to do?

[dmcole]

Ladyada: Thanks for your insight. From another board I got the CLI for the fuse bits. When I get some new 8515s I'll use that, abandoning AVRFuses for the moment.

SS: This is for a DMX transceiver: http://www.hoelscher-hi.de/hendrik/english/dimmer.htm

[karlgg]

There was a link I had about feeding mis-fused AVRs a clock signal with the programmer... But I don't know what I did with it. If you know (or think you know) what the fuses were set to, you could hook up the clock circuit it's expecting just to let it run long enough to reprogram (back to the default internal clock, or what you intended originally).

[Sorceress Sarah]

I wonder if I dare. . .?

A few app notes that might interest you. . .
With reference designs!

[karlgg]

Okay, that confuses me. How are dimmer circuits from Cyprus supposed to help reprogramming a mis-programmed Atmel chip?

[Sorceress Sarah]

Okay, that confuses me. How are dimmer circuits from Cyprus supposed to help reprogramming a mis-programmed Atmel chip?

The point was to give a

Code: Select all

char * data;

about some bugs that are specifically designed for the purpose, as well as a pretty darned slick controller (think iPod), as well as the reference designs to accomplish the job.

The suggestion is that while you can frequently get that screw on your glasses tight with the end of s butterknife, sometimes its best to get the jewler's screwdriver.

[dmcole]

I wonder if I dare. . .?

A few app notes that might interest you. . .
With reference designs!

Way over my head. But thanks for taking the time to provide the link.

\dmc

[dmcole]

you want Ext Crystal, not RC osciallator

Just for clarity's sake ...

When I go to http://www.engbedded.com/fusecalc

and pick an ATmega8515, under the "features" pull-down menu, what should I pick for an 8MHz external crystal?

Thanks.

\dmc

[adafruit]

what does the datasheet suggest?

[dmcole]

what does the datasheet suggest?

The datasheet I have -- 2512J–AVR–10/06 -- discusses crystal oscillators on Pages 35-38. In the text on Page 36, it says that "The Oscillator can operate in three different modes, each optimized for a specific frequency range." It then shows Table 7 with -- four different modes. OK, obviously the first and fourth modes are the same thing, one for a resonator and one for a crystal, but jeez, gimme a break.

Anyway, nowhere in the datasheet does it define "low frequency," "medium frequency" or "high frequency," which are the phrases used by the fusecalc page. I have read somewhere -- I can't find it now, a random web page that sticks in my memory, if not Google's -- that "medium" is 3-8 and "high" is >8, but if you have an 8MHz crystal, is it medium or high?

Insofar as the startup times go, it seems the data sheet (Table 9) is recommending a 16K; my guess is that since the default reset time is 4ms that will suffice in a production environment as well.

So, that leaves two choices:

*Ext. Crystal/Resonator Medium Freq.; Start-up time: 16K CK + 4 ms; [CSEL=1101 SUT=10]
*Ext. Crystal/Resonator High Freq.; Start-up time: 16K CK + 4 ms; [CSEL=1111 SUT=10]

\dmc

[adafruit]

i think either one you pick should be just fine

[dmcole]

i think either one you pick should be just fine

I chose the first one and it appears to have worked.

Thanks.

\dmc