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i2C clock Speed

 
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i2C clock Speed
PostPosted: Mon Aug 16, 2004 1:03 pm     Reply with quote
Hi all,

I use formula osc/4 * (SSPADD+1) to get the colck speed I want.

Code as folows:
Code:

#include <16f877.H>
#fuses hs, NOPROTECT, BROWNOUT, PUT, NOWDT, NOLVP
#use delay(clock= 20000000)
#use i2c(Master,fast,sda=PIN_C4, scl=PIN_C3, FORCE_HW)

//========================
#byte SSPADD = 0x93
main ()
{
SSPADD = 0x20;   
output_float(PIN_C3);
output_float(PIN_C4);
i2c_start();
i2c_write(0x1E);
i2c_write(0x0f);
i2c_start();
i2c_write(0x1f);
i2c_read(0);
i2c_stop();
while(1)
{
;

}

}


Here is the result I got

SSPADD cloock Speed Formula
B 385KHZ 417KHZ
C 357KHZ 385KHZ
D 333KHZ 357KHZ
20 147KHZ 333KHZ


It looks like if I change formula to OSC/4*(SSPADD+2), results match formula.

I use 1 K pull up resistor, will this affect speed?

Thanks in advance

Minmin
valemike
Guest
PostPosted: Mon Aug 16, 2004 3:53 pm     Reply with quote
I think the pullup resistor only affects how long it takes to swing the logic level up and down. As long as this swing happens well ahead of time for the rate of the SCL, in time for SDA to sample an unambiguous level, you should be fine, I think. Someone correct me if i'm wrong.
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