why the value 1275 is used in this function?

[regin]

hi,

i am a beginner in microcontroller and embbeded c.

///// please help me/////

why 1275 value selected in this fuction?

void delay(unsigned int msec)
{
int i,j;
for(i=0;i<msec;i++)
for(j=0;j<1275;j++);
}

what is the logic behind this?

i am using AT89s52 .... frequency set to 11.0592 mhz.

 

[doraemon]

Hello!

Probably because the guy who wrote the function tried a few values and ended up with
1275 as the closest number of loops to make 1 millisecond.
It sounds like an odd value, anyway. 11.0592 MHZ divided by 1275 makes 8674.
With a value very close to 9000 for instance, I would guess that 1 loop takes 9 clocks.
By the way, I suppose you took the code as is from another implementation that was
working with another crystal, right?

Dora.

 

[Taner]

Probably 1msec=1275x(Instruction Period)

 

[doraemon]

Hello!

Just a remark about your code above.

Writing a raw value (like this 1275) is just a sign of a poorly written code.
What you should do is:

#define LOOPS_PER_MS 1275 // Number of loops per millisecond

and later for(j = 0 ; j < LOOPS_PER_MS ; ++j)

Doing this, you will have no trouble to understand what you wrote even
a few months later, and on top of that other people will also understand
what you wrote.

Dora.