delay calculation help

[georgetwo]

hi
im new to pic programming, I saw a led c project online which worked well on my pic18f4550 but i want to edit the time delay. I need help in calculating the delay with respect to any osc. in c im using 12MHz crystal
Thanks

 

[ericgibbs]

hi
im new to pic programming, I saw a led c project online which worked well on my pic18f4550 but i want to edit the time delay. I need help in calculating the delay with respect to any osc. in c im using 12MHz crystal
Thanks

hi,
Look at this calculator link.
http://www.biltronix.com/picloops.html

 

[georgetwo]

from the link, I think it is for Assembler only or does it work on C also?

 

[Pommie]

Most C compilers have a delay library.

Mike.

 

[AtomSoft]

OK for PIC its simply :

1 CYCLE = 1/(FOSC/4)

example: 1 Cycle for a 12Mhz Clock on a PIC would be = 1/(12000000/4) = 1/3000000 = 0.000 000 3 = 300ns

so now that you have one cycle.. which here is 300ns. to make a delay for 100us we have to divide

100us / 300ns = 0.0001 / 0.0000003 = 333 .. thats how many cycles it takes to make 100us delay...

So if we delay 333 cycles its a 100us delay...

Understand it?

 

[georgetwo]

whith tha fomular, 1sec.= 1/300ns =3333333cycles
this gave me outrageous time. this is the time code

void Wait()
[
unsigned char i;
for (i=0;i<100;i++)
_delay(60000);
]
how do i calculate the delay time and adjust to the value i want?
thanks 4 your help so far

 

[AtomSoft]

ok exactly 12mhz = 3 mhz internal clock:

1/3Mhz = 3.333333333333333e-7 = 0.0000003333333333333333

which is 0.0000003333333333333333 aka 333.3333333333333ns each cycle

1 second = 1 / 333.3333333333333ns = 3000000.0003= 3,000,000 Cycles... and yes its correct... check out this link:




To Calc it on the fly make some functions like ...

1 second = 3,000,000 cycles
1 millisecond = 3,000 cycles
1 microsecond = 3 cycles

Make loops for each like:

void delay_ms(int time)
{
    int i;
    for (i=0;i<time;i++)
    _delay(30000);
}

Now you can delay 10 ms with : delay_ms(10);

Be aware it wont be 100% accurate since you have to calculate how long it takes to make the call to the function... how long it takes for 1 loop and then to leave the function. But if 1ms off is ok im sure this will do