setsclhigh.c

一个AVR单片机at17c85的系统程序

// SetSCLHigh.c
// Det SCL high, and wait for it to go high.
// Returns the value of t0_timed_out. If 0xff then we timed out before SCL went high and
// should be used to indicate an error to the caller
// Crystal frequency is 7.3728 MHz

#include "at17c.h"

extern volatile unsigned char t0_timed_out;

extern void WriteSCL(unsigned char state);

unsigned char SetSCLHigh(void) {

    WriteSCL(1); // release SCL

    // set up timer counter 0 for timeout
    t0_timed_out = FALSE; // will be set after approximately 34 us
    TCNT0 = 0; // clear counter
    TCCR0 = 1; // ck/1 ..  enable counting

    // wait till SCL goes to a 1
    while (!(PINB & 0x02) && !t0_timed_out);

    TCCR0 = 0; // stop the counter clock

    return(t0_timed_out);

}