AVR-Chat

Hi Guys,

Thanks for the suggestions but I'm still not seeing the change in the
clock.  If I set the 9.6MHz fuse my circuit will use 5.1ma.  If I
change the fuse to the 4.8MHz choice my circuit will draw 3.6ma.  No
matter what I use for the CLKPR register values my program isn't
changing the clock.  I'm writing an 0x80 to the register and the next
instruction is the CLKPR = 0x03 so it should be meeting the 4 cycle
restriction as stated in the manual.

Thanks,

Richard Cooke


-- In AVR-Chat@yahoogroups.com, "Larry Barello" <yahoo@...> wrote:
>
> I recently went through this exercise on the mega88.  In short, it works
> great, but I would check for any errata on the tiny13 regarding that
option.
> 
> My problem, it turned out, had nothing to do with the clock change,
but in
> recording whether I was running at high speed or not.  My logic got
out of
> synch.  I switch from CLK/2 to CLK/256 which has a dramatic effect on
> current draw.
> 
> Anyway, you need to make sure the two instructions follow each other.
> Inspect the generated assembly code (assuming this is avr-gcc) to
verify.
> Another thing you can do is toggle an output pin and directly verify the
> clock change.  Depending upon your code, you might protect them with an
> CLI/SEI pair.
> 
> Finally, make sure that hooking up the dragon (in debug mode) that
doesn't
> mess up your expected current draw.  I did all my measurements with the
> one-wire debugger disabled.
> 
> -----Original Message-----
> From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On
Behalf
> Of Richard Cooke
> Sent: Monday, November 20, 2006 9:23 PM
> To: AVR-Chat@yahoogroups.com
> Subject: [AVR-Chat] How do you change the clk speed?
> 
> Hi Folks,
> 
> I'm working on the ATtiny13 with the AVR Dragon and the latest version
> of AVR Studio (4.12 SP4).  I guess I don't understand how to change
> the clock frequency correctly.  I read the manual and I thought that
> if I used:
> 
> CLKPR=0x80;  // enable the Clock Prescaler Change Enable bit
> CLKPR=0x02;  // system clock divide by 4
> 
> Isn't this the proper way to change the clock?  I'm measuring the
> current and I see no change.  I'm running the chip at 5V and according
> the the spec sheet I should measure a little over 1ma at 1.2MHz.
> 
> Any ideas?
> 
> Thanks,
> 
> Richard Cooke
> 
> 
> 
> 
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