Hello!

MPLABX, PIC18F16Q40, I2C, MLX90614 sensor.

To get the correct result from the sensor, a Repeated Start required in the communication sequence. Whith this new type of I2C module, i don't know how to do that. Attached the read code which is using Stop and Start instead of Repeated Start. Without the correct communication i got only 0xFFFF.

Can somebody tell me, how to modify the code?

See picture, what is the difference between the good (PIC18F14K22) and the not good communication.

Thank you!

    extern volatile uint8_t mlx_msb, mlx_lsb;
    
    static inline void wait4stop(void) {
        while (!I2C1PIRbits.PCIF);
        I2C1PIRbits.PCIF = 0;
        I2C1PIRbits.SCIF = 0;
        I2C1STAT1bits.CLRBF = 1;
    }
    
    void read_mlx(void) {
    
        I2C1CNTH = 0;
    
        I2C1TXB = 0xB4; //write address
        I2C1CNTL = 1;
        I2C1CON0bits.S = 1;
        while (!I2C1STAT1bits.TXBE);
        I2C1TXB = 0x07; //RAM Tobj1
        while (!I2C1STAT1bits.TXBE);
    
        wait4stop();
    
        I2C1TXB = 0xB5; //read address
        I2C1CNTL = 0;
        I2C1CON0bits.RSEN = 1;
        I2C1CON0bits.S = 1;
        while (!I2C1CON0bits.MDR);
        I2C1CNTL = 2;
        I2C1CON0bits.S = 1;
        I2C1CON0bits.RSEN = 0;
    
        while (!I2C1STAT1bits.RXBF);
        mlx_lsb = I2C1RXB; //LSB
        while (!I2C1STAT1bits.RXBF);
        mlx_msb = I2C1RXB; //MSB
    
        wait4stop();
    
    }

 

Got some help from other source. The correct sequence:

extern volatile uint8_t mlx_msb, mlx_lsb;

static inline void wait4stop(void) {
    while (!I2C1PIRbits.PCIF);
    I2C1PIRbits.PCIF = 0;
    I2C1PIRbits.SCIF = 0;
    I2C1STAT1bits.CLRBF = 1;
}

void read_mlx(void) {

    I2C1CNTH = 0;

    I2C1TXB = 0xB4; //write address
    I2C1CNTL = 1;
    I2C1CON0bits.S = 1;
    while (!I2C1STAT1bits.TXBE);
    I2C1TXB = 0x07; //RAM Tobj1
    while (!I2C1STAT1bits.TXBE);

    I2C1CON0bits.RSEN = 1;
    I2C1CON0bits.S = 1;
    while (!I2C1CON0bits.MDR);

    I2C1TXB = 0xB5; //read address
    I2C1CNTL = 0;
    I2C1CON0bits.S = 1;
    while (!I2C1CON0bits.MDR);

    I2C1CNTL = 2;
    I2C1CON0bits.S = 1;

    while (!I2C1STAT1bits.RXBF);
    mlx_lsb = I2C1RXB; //LSB
    while (!I2C1STAT1bits.RXBF);
    mlx_msb = I2C1RXB; //MSB

    while (!I2C1CON0bits.MDR);
    I2C1CON1bits.P = 1;
    wait4stop();

}