oscillator clock and delay

[Guest]

Iam a newbie to microcontrollers and PIC's

I am using
16F870
MPLAB v6.60
PIC Start Plus
PIC C Compiler

I want to know the relationship between the
Oscillator frequency,
# use delay(clock = ...........) and
delay_ms(......) functions in PICC compiler

Couldnot find any where, any help is appreciated....

Thanks,

[rwyoung]

The delay_ms() and delay_us() functions need to know the clock oscillator speed so the compiler can configure the functions and the function calls appropriately.

Enter the wrong value for #use delay(clock=#####) and your software delays (and probably software UART too) will be off by the ratio of the actual clock speed and what you entered.
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Rob Young
The Screw-Up Fairy may just visit you but he has crashed on my couch for the last month!

[theMagni]

All you have to do is put in the speed of your oscillator in the delay block, and then when you call the function delay_ms(X) or delay_us(X), you delay by X ms or us.

So, for a 4MHz clock, you just put this line somewhere:
#use delay( clock=4000000 )

I put mine up at the top near the #defines, but it's up to your coding style.

From then on in the code, you can just include the line:
use_delay( 500 );

to wait for 1/2 a second. 500 can be any long value.

Note that your watchdog timer may go off during a delay loop. You can change the line to this:
#use delay( clock=4000000, RESTART_WDT )
to prevent that. I had horrible problems resetting my WDT with the #use delay.

You can check out the manual under "#use delay" for more details.
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In the 90's, I promised myself I'd never use a so-called "smiley icon". I hate what I've become. ;)