I2C is a multi-master serial single-ended bus invented by Philips that is used to attach low-speed peripherals to an embedded system. SMBus, defined by Intel in 1995, is a subset of I2C. This article is a practical guide to use the I2C bus on the CORE9G25 Systems Linux embedded boards

• Read more about I2C bus on Wikipedia...

To have a more in depth idea of how the I2C works under Linux please read the Linux Kernel documentation on:

• I2C bus Kernel documentation

 C code example

The following example sends a sequence of values from 0 to 255 to the PCF8574 I2C I/O expander at address 0x20 in C language.

• write.c This code example is downloadable from the CD. File: CD: /linux/example/i2c/write.c

  #include 
  #include 
  #include 
  #include 
  
  #define I2C_ADDR 0x20
   
  int main (void) {
  	int value;
  	int fd;
  
  	fd = open("/dev/i2c-0", O_RDWR);
  
  	if (fd < 0) {
  		printf("Error opening file: %s\n", strerror(errno));
  		return 1;
  	}
  
  	if (ioctl(fd, I2C_SLAVE, I2C_ADDR) < 0) {
  		printf("ioctl error: %s\n", strerror(errno));
  		return 1;
  	}
  
  	for (value=0; value<=255; value++) {
  		if (write(fd, &value, 1) != 1) {
  			printf("Error writing file: %s\n", strerror(errno));
  		}
  		usleep(100000);
  	}
  	return 0;
  }
  

Related links

• I2C python documentation
• I2C bus Kernel documentation
• I2C bus Wikipedia definition