diff --git a/include/zh_avr_i2c.h b/include/zh_avr_i2c.h
index df55eb2..e40ae24 100644
--- a/include/zh_avr_i2c.h
+++ b/include/zh_avr_i2c.h
@@ -29,12 +29,29 @@ extern "C"
 		AVR_ERR_NOT_ALLOWED
 	} avr_err_t;
 
+	/**
+	 * @brief Initialize I2C bus.
+	 *
+	 * @param[in] pullup Using internal pullup resistors.
+	 *
+	 * @return AVR_OK if success or an error code otherwise.
+	 */
 	avr_err_t zh_avr_i2c_master_init(const bool pullup);
+
+	/**
+	 * @brief Probe I2C address, if address is correct and ACK is received, this function will return AVR_OK.
+	 *
+	 * @param[in] addr Address I2C device address that you want to probe.
+	 * @param[in] xTicksToWait Wait timeout in FreeRTOS ticks.
+	 *
+	 * @return AVR_OK if success or an error code otherwise.
+	 */
 	avr_err_t zh_avr_i2c_master_probe(const uint8_t addr, TickType_t xTicksToWait);
 	avr_err_t zh_avr_i2c_master_transmit(const uint8_t addr, uint8_t *data, uint8_t size, TickType_t xTicksToWait);
 	avr_err_t zh_avr_i2c_master_receive(const uint8_t addr, uint8_t *data, uint8_t size, TickType_t xTicksToWait);
-	avr_err_t zh_avr_i2c_master_transmit_register(const uint8_t addr, uint16_t *reg, uint8_t *data, uint8_t size, TickType_t xTicksToWait);
-	avr_err_t zh_avr_i2c_master_receive_register(const uint8_t addr, uint16_t *reg, uint8_t *data, uint8_t size, TickType_t xTicksToWait);
+
+	avr_err_t zh_avr_i2c_master_transmit_register(const uint8_t addr, uint16_t *reg, uint8_t *data, uint8_t size, TickType_t xTicksToWait); // To Do
+	avr_err_t zh_avr_i2c_master_receive_register(const uint8_t addr, uint16_t *reg, uint8_t *data, uint8_t size, TickType_t xTicksToWait);	// To Do
 
 #ifdef __cplusplus
 }