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igorfcardoso
PostPosted: Mar 06, 2009 - 06:49 PM
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Joined: Mar 02, 2009
Posts: 23


Hi,

I was reading the ATTiny85 datasheet and found out that the I/O pin from Reset is not usable as I thought.

I really need another I/O, but if I disable the Reset pin by Fuse will make my ATTiny85 unprogrammable forever?

Thanks,

Igor.
 
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jayjay1974
PostPosted: Mar 06, 2009 - 07:21 PM
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You will need to use high voltage programming to reset the fuse, so it's not permanent. It will make debugging and programming quite hard.
 
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igorfcardoso
PostPosted: Mar 06, 2009 - 07:26 PM
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How to reset the fuses using high voltage programming? Is there any tutorial?

Thanks for your quick answer.

Igor.
 
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glitch
PostPosted: Mar 06, 2009 - 07:38 PM
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you will need a programmer capable of delivering +12V to the reset pin. One important thing to note... make sure that whatever you have connected to that pin is also capable of handling that +12V signal.
 
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danni
PostPosted: Mar 06, 2009 - 08:02 PM
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igorfcardoso wrote:
I really need another I/O, but if I disable the Reset pin by Fuse will make my ATTiny85 unprogrammable forever?


No.
For reprogramming burn a bootloader into the AVR prior disabling the reset pin.


Peter
 
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Koshchi
PostPosted: Mar 06, 2009 - 08:48 PM
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Joined: Nov 17, 2004
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Quote:
For reprogramming burn a bootloader into the AVR prior disabling the reset pin.

This assumes that you have a pin set up as a UART receive (or some other input method). If that is not the case, then a bootloader will not help since you would need yet another pin available.

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digitool
PostPosted: Mar 06, 2009 - 09:01 PM
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Depending on what you are trying to do a pin can have a dual purpose :for example blinking an led and reading a pushbutton. Just what is hooked up to your pins?
 
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danni
PostPosted: Mar 06, 2009 - 09:13 PM
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Koshchi wrote:
This assumes that you have a pin set up as a UART receive (or some other input method).


Yes, thats the big advantage of the bootloader.
You need only share a single pin with the application instead four pins on SPI-programming.

E.g. your application use a push button, then this pin can be shared with the bootloader.
Simple press not the button during download a new application.

Or another approach, use a three pin header. For running the application a jumper was placed to connect the pin with the application.
And for download the jumper was removed and a two wire cable was connected with the PC COM port or an USB-COM dongle.


Peter
 
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igorfcardoso
PostPosted: Mar 09, 2009 - 06:04 PM
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Joined: Mar 02, 2009
Posts: 23


Problem solved. I figure out a way to use one pin for two functions and worked fine, like digitool sugested.

The solution with bootloader is not bad, but will be too complicated for my application.

Thanks all for the sugestions.

Igor.
 
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