micro second delay for 89V51RD2

Status
Not open for further replies.
C

chethankp

Member level 4
Joined
Jan 4, 2010
Messages
76
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,286
Location
bangalore
Visit site
Activity points
1,860
Hi,
I am using 89V51RD2 for some application .. I need to write delay code which can take create micro second delay ..

I wrote the below code

void delayMicroseconds(unsigned int i)
{

for(j=0;j<=i;j++)
{

for(k=0;k<256;k++);
}

}

But I do not think this is giving correct micro second delay .

Someone suggested to use the micro time for delay ..

I did not understand how exactly I can use the timer for it .
becoz I need to use the delayMicroseconds() from many places with different values .

like
delayMicroseconds(1);

delayMicroseconds(10)
delayMicroseconds(25)

Can somebody suggest a method to get exact micro second delay ..

?
 

hi there are lot of delay routines in lot of compilers with knowing the clock frequency... For creating exact delay in a C program without any inbuilt functions you have to work some more. . .
write the 
Code C - [expand]
1

for(k=0;k<10;k++);

and decode it as assembly and find how many instructions written for it.. then change the value 10 according to your 1 us...
If you need more accuracy and less work, put a break point on this line and after this line now run and find how many instruction cycles taken for....
Or if you use keil _nop_ () function can give the delay of 1 instruction cycle with this you can create 1 us delay and loop it, but looping nop instruction for 1us is not recommended..
 
if you are using 20MHz crystal then try

Code: 
void DelayMicroSeconds (int us)
{
        for( ; us>0 ; us--)
        {
          _nop_();               // if crystal is 20Mhz then delay is 10 microsecond
          _nop_();
          _nop_();
          _nop_();   
        }
}

and also try Venkadesh_M suggest as match perfect instruction cycle to put nop() in your routin..
 
Hi, the micro controller board which I bought has 11MHz ... and I don't have debugger to check the exact time for each instruction ...

Will adding two more _nop_ in to your suggested cide will create a 10micro second delay?
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…