question about atmega1284P fuses

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aliyesami

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I am going to be programming this chip via Pololu ISP programmer . I want to use the external crystal oscillator do I need to program any fuses for this ?
I used atmel328 before brand new chip and I burned the bootloader and sketches on it via arduino and I didn't burn any fuses but the datasheet for atmega1284P is saying that by default internal clock is used which is only 1Mhz , I will be using 20Mhz crystal .

thanks
 

wp100 said:
Hi,

The Arduino does everything for you.

Stand alone programming will require Fuses , this should help
https://www.engbedded.com/fusecalc
Click to expand...

when I uploaded my atmega328P via arduino how did arduino setup the fuses since I never specified them?
I know the engbedded utility its for getting the right fuse values for the avrdude.

I have a feeling that my sketches were working cause the internal divided clock of 1Mhz was used and not the external 16Mhz crystal I put , right?
 


Hi,

Its a while since I did any stand alone programming /fuses using an usbisp device, though think you may be using Studio with that Pololu programmer which has a fuse sub menu ?

Think this thread will answer your questions.
https://forum.arduino.cc/index.php?topic=71580.0
 

Its better if you use the internal clock oscillator because for external clock source you have to program the low byte fuse and it is also more costly...
 


http://www.atmel.com/images/doc8059.pdf


In order to use the external crystal you have to set the fuses accordingly (and disable CKDIV8), refer to section 7.4 Full Swing Crystal Oscillator
 
JAMAL JIMI said:
Its better if you use the internal clock oscillator because for external clock source you have to program the low byte fuse and it is also more costly...
Click to expand...

costly? in which sense ?
I think its a huge advantage in running with 20Mhz external crystal than 1Mhz internal clock .
 

Using the internal RC clock is an entirely different story, first of all it limits you to 8Mhz and secondly it has a quite high tolerance (compared to a 0.00005% of a crystal) plus it changes with the voltage supply level.
Depending on the application this may or may not be a problem.



 

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