diff --git a/i2c.c b/i2c.c
index 6d54baf..5aada81 100644
--- a/i2c.c
+++ b/i2c.c
@@ -16,7 +16,15 @@
 #endif
 
 uint8_t I2C_ErrorCode;
-
+/**********************************************
+ Public Function: i2c_init
+ 
+ Purpose: Initialise TWI/I2C interface
+ 
+ Input Parameter: none
+ 
+ Return Value: none
+ **********************************************/
 void i2c_init(void){
     // set clock
     switch (PSC_I2C) {
@@ -37,6 +45,16 @@ void i2c_init(void){
     // enable
     TWCR = (1 << TWEN);
 }
+/**********************************************
+ Public Function: i2c_start
+ 
+ Purpose: Start TWI/I2C interface
+ 
+ Input Parameter:
+ - uint8_t i2c_addr: Adress of reciever
+ 
+ Return Value: none
+ **********************************************/
 void i2c_start(uint8_t i2c_addr){
     // i2c start
     TWCR = (1 << TWINT)|(1 << TWSTA)|(1 << TWEN);
@@ -62,10 +80,29 @@ void i2c_start(uint8_t i2c_addr){
 		}
 	};
 }
+/**********************************************
+ Public Function: i2c_stop
+ 
+ Purpose: Stop TWI/I2C interface
+ 
+ Input Parameter: none
+ 
+ Return Value: none
+ **********************************************/
 void i2c_stop(void){
     // i2c stop
     TWCR = (1 << TWINT)|(1 << TWSTO)|(1 << TWEN);
 }
+/**********************************************
+ Public Function: i2c_byte
+ 
+ Purpose: Send byte at TWI/I2C interface
+ 
+ Input Parameter:
+ - uint8_t byte: Byte to send to reciever
+ 
+ Return Value: none
+ **********************************************/
 void i2c_byte(uint8_t byte){
     TWDR = byte;
     TWCR = (1 << TWINT)|( 1 << TWEN);
@@ -79,6 +116,17 @@ void i2c_byte(uint8_t byte){
 		}
 	};
 }
+/**********************************************
+ Public Function: i2c_readAck
+ 
+ Purpose: read acknowledge from TWI/I2C Interface
+ 
+ Input Parameter: none
+ 
+ Return Value: uint8_t
+  - TWDR: recieved value at TWI/I2C-Interface, 0 at timeout
+  - 0:    Error at read
+ **********************************************/
 uint8_t i2c_readAck(void){
     TWCR = (1<<TWINT)|(1<<TWEN)|(1<<TWEA);
     uint16_t timeout = F_CPU/F_I2C*2.0;
@@ -92,6 +140,18 @@ uint8_t i2c_readAck(void){
 	};
     return TWDR;
 }
+
+ /**********************************************
+ Public Function: i2c_readNAck
+ 
+ Purpose: read non-acknowledge from TWI/I2C Interface
+ 
+ Input Parameter: none
+ 
+ Return Value: uint8_t
+  - TWDR: recieved value at TWI/I2C-Interface
+  - 0:    Error at read
+ **********************************************/
 uint8_t i2c_readNAck(void){
     TWCR = (1<<TWINT)|(1<<TWEN);
     uint16_t timeout = F_CPU/F_I2C*2.0;
@@ -100,7 +160,7 @@ uint8_t i2c_readNAck(void){
 		timeout--;
 		if(timeout == 0){
 			I2C_ErrorCode |= (1 << I2C_READNACK);
-			return 0;
+            return 0;
 		}
 	};
     return TWDR;