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#use delay() differences compared to just fuses

 
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pfournier



Joined: 30 Sep 2003
Posts: 89

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#use delay() differences compared to just fuses
PostPosted: Fri May 02, 2014 1:51 pm     Reply with quote
18F87j50
CCS compiler 5.025

I had an issue with some code where changing the processor speed would give the the wrong baud rate (and timer rate).

I finally built a very simple led flasher with RS232 printf statements.

I used the wizard and found it created a statement:
Code:
#use delay(clock=48000000,oscillator=12000000)

and the code worked!

If I used:
Code:

#fuses PLL3, NOCPUDIV, ECPLL
#use delay(clock=48000000)

and the code did NOT work.

The fuses as shown in the LST file were identical, but there were code differences.
Code:

Configuration Fuses:
   Word  1: F7AA   NOWDT PLL3 STVREN NOXINST NODEBUG NOCPUDIV NOPROTECT
   Word  2: F7C7   ECPLL FCMEN IESO WDT128
   Word  3: FFF8   EASHFT MCU BW16 NOWAIT CCP2C1 ECCPE PMPEMB MSSPMSK7

While I could probably figure out the purpose of the differences, given enough time, I was hoping someone would know what the additional code does, and how, if not for accidentally finding this use delay option, I would never have known this.

Now I could swear this worked ok when I was using version 4.xxx, but I will have to take a trip down memory lane to check that out.
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Ttelmah



Joined: 11 Mar 2010
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PostPosted: Sat May 03, 2014 12:22 am     Reply with quote
You'll find the extra code, is the equivalent of adding 'setup_oscillator(OSC_NORMAL)'.

This type of behaviour is getting more common (especially on the PIC24's), where as well as setting the fuses, there has to be a configuration of some registers to setup the clock. The extended clock statement, tries (for instance) to setup the PLL used on these, while the simpler clock statement leaves this unconfigured.
Generally, on the later compilers it is safer to use the extended clock setup, and only get involved in the manual clock fuses if this doesn't work right.

Best Wishes
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