See Also Arduino and MPU6050 Accelerometer and Gyroscope TutorialДЇor the GY-521 breakout board we have only one address and thatвЂ™s a hexadecimal 0ењ†8. So we can get data from 8 different sensors with just two wires with the I2C bus. ExampleДЄs an example I will use the GY-80 breakout board which consists 5 different sensors and the GY-521 breakout board which consists 3 different sensors. After the data is completely sent, the transfer will end with a stop condition which occurs when the SDA line goes from low to high while the SCL line is high. These addresses can be found from datasheet of the sensor.ДЄfter the addressing, the data transfer sequences begin either from the master or the slave depending of the selected mode at the R/W bit. So if we want to read the data of the X-axis, first we need to send the device address and then the particular internal register address for the X-axis. For example the ADX345 Accelerometer has a unique device address and addition internal registers addresses for the X, Y and Z axis. The internal registers are locations in the slaveвЂ™s memory containing various information or data. Next is the internal registers addressing.

The device addressing sequence stars with the most significant bit (MSB) first and ends with the least significant bit (LSB) and itвЂ™s actually composed of 7 bits because the 8 th bit is used for indicating whether the master will write to the slave (logic low) or read from it (logic high). After this the clock starts and each data bit is transferred during each clock pulse. The start condition occurs when data line drops low while the clock line is still high.

LetвЂ™s take even closer look at these events. Right after the addressing sequences follows the data sequences as many until the data is completely sent and it ends with a special stop condition. After the first Acknowledge bit in most cases comes another addressing sequence but this time for the internal registers of the slave device. After each 8 bits sequence follows a bit called Acknowledge. So after a special start condition occurs comes the first 8 bits sequence which indicates the address of the slave to which the data is being sent. You can check the examples in the examples/communication folder to understand better how this works.The data signal is transferred in sequences of 8 bits. The second class, ofArduino, is specific to the arduino, it uses a protocol called firmata to send messages to and from the arduino that way you don't need to care about implementing the communication protocol from the Arduino sketch to openFrameworks and viceversa but instead you can just send and read values directly to and from any pin in the Arduino. It also works the other way around, you can send messages from the Arduino (or any other serial device), for example the read from a temperature sensor to openFrameworks. It can be used to send custom commands to for example an Arduino sketch that will receive them and do something in response like turn an LED on, move a motor. There's 2 classes in this module, ofSerial which allows to communicate with any device through the serial protocol. This mainly allows to communicate with devices like the Arduino. The communication module has classes to communicate with other devices by now through the serial protocol.

Arduino and other serial devices communication.

Arduino serial communication protocol