What is I2S?
The I2S (Inter-Integrated Circuit Sound) protocol is a serial communication protocol commonly used for transmitting digital audio data between integrated circuits (ICs) in audio systems. It was developed by Philips Semiconductor (now NXP Semiconductors) in the 1980s.
I2S is primarily designed for transmitting audio data, including both the digital audio samples and the timing information needed for synchronization. It uses separate lines for data, clock, and word select signals, allowing for a straightforward and efficient transmission of audio data.
The I2S protocol has become widely adopted in the audio industry and is commonly used in various applications, including digital audio interfaces, digital signal processors (DSPs), audio codecs, and audio digital-to-analog converters (DACs). It is particularly prevalent in audio applications that require high-quality sound reproduction, such as professional audio equipment, consumer audio devices, and musical instruments.
While Philips Semiconductor (now NXP Semiconductors) invented the I2S protocol, it has since become a widely adopted industry standard. Many semiconductor manufacturers and audio device manufacturers implement and support the I2S protocol in their products, ensuring compatibility and interoperability across different devices.
In the I2S protocol, data, clock, and word select lines serve specific purposes in the transmission of digital audio data. Here's a brief explanation of each:
Data Line: The data line (often labeled as "SD", "SDIN" or "SDATA") is responsible for carrying the actual digital audio samples. It transmits the binary representation of the audio data, which can be in various formats such as PCM (Pulse Code Modulation) or PDM (Pulse Density Modulation). The data line carries the audio information in a serial fashion, with each audio sample being sent sequentially.
Clock Line: The clock line (often labeled as "SCK" , "BLCK" or "SCLK") provides the timing reference for the transmission of data. It generates a continuous clock signal that synchronizes the sending and receiving devices. The clock signal ensures that the data is sampled and interpreted at the correct rate, allowing for accurate reconstruction of the audio signal at the receiving end. The clock line's frequency is determined by the sampling rate of the audio data.
Word Select Line: The word select line (often labeled as "WS" "LRCLK"
or "LRCK" for Left/Right Clock) indicates the start of a new audio word or frame. It determines whether the current data being transmitted represents the left channel or the right channel of the audio signal. The word select line switches between high and low states to indicate the alternating left and right audio channels. This information is crucial for the receiving device to properly demultiplex the data and correctly reproduce the stereo audio signal.
Together, these three lines (data, clock, and word select) enable the accurate and synchronized transmission of digital audio data in the I2S protocol.
Many microcontroller units (MCUs) provide I2S support as it is a commonly used protocol in audio applications. Numerous MCU manufacturers offer devices with built-in I2S peripherals or modules. Some popular MCU families that provide I2S support include: ESP8266, ESP32, Raspberry Pi, Raspberry PI Pico.