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Updated CCS Software, 20MHz Circuit Runs at 6.63MHz?

 
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JV625



Joined: 25 Jun 2009
Posts: 16

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Updated CCS Software, 20MHz Circuit Runs at 6.63MHz?
PostPosted: Thu Dec 23, 2010 11:26 pm     Reply with quote

Hi Everyone,

I haven't used my ICD-40U or CCS compiler (PCWH) in a while, but I downloaded the update today and tried to debug a program that needs to run at 20+MHz on a 18F2450.

My circuit uses a 18F2450 with a 20MHz external oscillator, but when I tried to run code that I had with #use delay (clock=20000000) the printf statements would output gibberish.

I noticed in the debugger that it says "Ready MCU at 6.63MHz" and when I set the #use delay (clock=) to 6630000 the printf statements worked properly.

The only problem is, it seems like the program runs too slow.

Any idea how to debug it at a full 20MHz or if I perhaps have some setting wrong? I never saw this 6.63MHz thing before in the prior version.

Thanks!
newguy



Joined: 24 Jun 2004
Posts: 1447
Location: Edmonton, Alberta

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PostPosted: Fri Dec 24, 2010 11:17 am     Reply with quote

Did your supply voltage (Vcc) change as well? I don't think that all of the LF parts do this, but many do - as the supply voltage drops, the maximum processor speed drops too.
JV625



Joined: 25 Jun 2009
Posts: 16

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PostPosted: Fri Dec 24, 2010 4:21 pm     Reply with quote

Not that I know of, and so far I've tried it with two different circuit boards and power supplies ... one at 6V and one at 5V.

Additionally, I am noticing that the fuses I set in the code will change the speed, but only between 5MHz and 6.63MHz.

If I use

#fuses HS

I get "Ready MCU at 4.98MHz"

If I use

#fuses HSPLL or no oscillator setting

I get "Ready MCU at 6.63MHz"

If I use

#fuses XT

I get an error message pop-up that says "Could not start target: The target was not halted after reset Check the target oscillator and MCLR. Make sure the target clock match the clock fuses and that the target is oscillating. Use View | Valid fuses to find the correct fuses."

Nothing seems to get me to 20MHz in this mode -- though one of the circuit boards, prior to my clearing it, was running an older program quite successfully at 20MHz.
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