AVR-Chat

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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