Antoniolinux B.

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8 years, 10 months ago.

MLX90614A and mbed library for i2c

Hi to all, Melexis Team! I'm sorry if my question is offtopic but i have this problem and i don't know to fix it. i write this easy program for read value from IR MLX90614A, i use stm32Nucleo L152re

title

#define I2C_WRITE   0
#define I2C_READ    1
int main() {
pc.printf("\nI2C start");
while(1) {
            char p1,p2,p3;

                 i2c.start();
                            int status=i2c.write((0x5A<<1)+I2C_WRITE);

                            int status2=i2c.write(0x07<<1);     
                        i2c.start();
                            int status3=i2c.write((0x5A<<1)+I2C_READ);  

                           p1=i2c.read(1);     //Tobj low byte
                            p2=i2c.read(1);     //Tobj heigh byte
                              p3=i2c.read(0);     //PEC
                            i2c.stop();
                            pc.printf("%d-", status);
                            pc.printf("%d-", status2);
                            pc.printf("%d-", status3);                  
                                    pc.printf("data-");
                            pc.printf("%d-", (int)p1);
                                pc.printf("%d-", (int)p2);
                                    pc.printf("%d-", (int)p3);
      wait(5);           // wait 5 seconds for next scan          
        }
    }

only status i see the ack, the 1 value the status2 and status3 i see 0 i dont' know where is the error because i read the your application note, can you help me? best regards A.

1 Answer

Wim Huiskamp
8 years, 10 months ago.

I dont have your devices, but general recommendation is to use the i2c block read and write operations instead of the byte wise operations. The byte operations are not well implemented on many platforms.

try something like this instead:

int main() {
pc.printf("\nI2C start");

  while(1) {
            char data[8];
  
            data[0]=0x07; // assume you are trying to write 0x07 as selected register

            // assume that 7bit slaveaddress is 0x5A, issue a repeated start
            int status = i2c.write((0x5A<<1), data, 1, true);

            // read the 3 data bytes, no need to set the LSB for read or write, that happens automatically
            int status3=i2c.read((0x5A<<1), data, 3);
 
            pc.printf("%d-", status);
            pc.printf("%d-", status3);                  
            pc.printf("data-");
            pc.printf("%d-", data[0]);
            pc.printf("%d-", data[1]);
            pc.printf("%d-", data[2]);
            wait(5);           // wait 5 seconds for next scan          
        }
 }

Accepted Answer

Hi Wim ,thanks for your answer now all work well, i have only i an question, i read 0 the value of status and status3, it's right or wrong best regards

posted by Antoniolinux B. 15 Dec 2015

The I2C API documentation may be found here. It states that the return values for blockread and block write methods are:

Returns: 0 on success (ack), non-0 on failure (nack)

So your status and status3 are correct.

posted by Wim Huiskamp 16 Dec 2015