Need simple question with I2C code!

[milem]

I need to know on what speed microkontroler 89S52 (24.000 MHz oscilator)
will communicate trough I2C bus using given code in atachment!

 

[laktronics]

Hi,
This I think it is not as simple a question as mentioned. However, the fastest duration at which data bits are shifted out will be decided by the execution time of the loop:

scl=0;
HOLD;
sda=MSB;
a<<=1;
_nop_();
scl=1;
HOLD;
scl=0;

Similarly, while receiving data, the execution time of the loop

sda=1;
scl=1;
HOLD;
LSB=sda;
if(i<7)
a<<=1;
HOLD;
scl=0;
HOLD;

will decide the time to receive each bit.

Hope it makes some sense to you.

Regards,
Laktronics

 

[milem]

Thanks for response, but!
Your response didn't help me!
I already know speed is coming from that loops, but i don't know how to calculate
that!
I don't know how long is single instructions are executed!
Does any know how to calculate that?

 

[drbizzarow]

best way to calculate real speed is, togle pin before and aftre the loop and use oscillscope to find pulse duration ..... i hope it will work

 

[milem]

That's good idea!
But i don't have good osciloscope to measure that! Thanks!

In short i need only to know are speed is under 400kHz!

 

[drbizzarow]

u can the try hit and trail method ..... if I2C works without delay its ok ...... if not then put delay steadly bw loop untill it start work ...... or use simulator.

 

[laktronics]

Hi,
Yes, the speed will be under 400KHz, since the clock Hi/Lo each has a 'Hold' delay which is equal to 3 NOPs and at 24MHz clock it works out to 1.5microsec. So, the maximum clock rate will be below 333kHz.

Regards,
Laktronics

 

[FL_KNV]

Keil has an excellent simulator. If you simulate the code, you will be able to see processor cycles, exact time period between clock cycle etc. Just calculate the frequency from time duration.