I am beginner at programming uC's. I have read all the tutorials on what is I2C and how it works, but I couldnt find any help specific on how to create a connection between my sensor and ATTiny88 (ATTiny88 datasheet.

I use SHT21 sensor (SHT21 datasheet) and want to communicate with ATTiny88 (MUC sends command to getData, and then sensors sends to MUC back the data (temperature, humidity)) - can someone help me guide through?

Once you help me, I'll understand it for future, but I really need a jump start here.



2 Answers 2


I have done I2C Communications for the Atmega32 and I interfaced a temperature sensor. Looking at the datasheet ATtiny and atmega has the same registers for I2C Communications. So you can use the following code I made for I2C Communication

This function will write the data to the I2C bus:

void i2c_write(unsigned char data)
  TWDR = data ;
  TWCR = (1<< TWINT)|(1<<TWEN);
  while ((TWCR & (1 <<TWINT)) == 0);

This function will start the I2C Communication:

void i2c_start(void)
  TWCR = (1 << TWINT) | (1 << TWSTA) | (1 << TWEN);
  while ((TWCR & (1 << TWINT)) == 0);

This function will stop the communication:

void i2c_stop()
  TWCR = (1<< TWINT)|(1<<TWEN)|(1<<TWSTO);

This function will initiate the I2C bus:

void i2c_init(void)

Now you can use these functions in you main

int main (void)
  return 0;

NOTE: Make the last bit of your address to 0 for writing and 1 reading from the i2c bus


you should try to check examples:


I see plenty of example on the I2C.

You should read them, understand them than try to implement them for your own application.

Regards, Mathieu L.

  • \$\begingroup\$ The probably i dont know which one of those documents i need to select. Because, unless i'm blind, i cannot find in titles of those docs "I2C communication" nor "communicating with sensor". You have to consider i'm a beginner in this, trying to learn before applying to university.. \$\endgroup\$ Commented Jun 17, 2015 at 22:06
  • \$\begingroup\$ Look in the brief descriptions, as well as the titles. Also, look for "TWI" (Two Wire Interface) - one description says "TWI (I2C compatible)". \$\endgroup\$ Commented Jun 17, 2015 at 22:38

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