Inter-Integrated Circuit Sound (I²S, I2S or IIS) is a serial bus for transmitting two-channel, digital audio as pulse-code modulation (PCM) between integrated circuit (IC) components of an electronic device. An I²S bus separates clock and serial data signals, resulting in simpler receivers than those required for asynchronous communications systems that need to recover the clock from the data stream.

Despite a similar name, I²S is unrelated to I²C.

History

The protocol standard was introduced in 1986 by Philips Semiconductor (now NXP Semiconductors) and was first revised on June 5, 1996. The standard was last revised on February 17, 2022 and updated terms master and slave to controller and target.

Details

thumb|500x500px|[[Digital timing diagram|Timing diagram of I²S]]

As shown in the diagram, the protocol requires the following lines:

  • Serial clock (SCK),
  • Word select (WS), but is commonly included for synchronizing the internal operation of the analog/digital converters
  • A multiplexed data line for upload

The bit clock pulses once for each discrete bit of data on the data lines. The bit clock frequency is the product of the sample rate, the number of bits per channel and the number of channels. So, for example, CD Audio with a sample frequency of 44.1 kHz, with 16 bits of precision and two channels (stereo) has a bit clock frequency of:

:44.1 kHz × 16 × 2 = 1.4112 MHz

The word select clock lets the device know whether channel 1 (WS = 0) or channel 2 (WS = 1) is currently being sent, because I²S allows two channels to be sent on the same data line. It is a 50% duty-cycle signal that has the same frequency as the sample frequency. For stereo material, the I²S specification states that the left audio is transmitted on the low cycle of the word select clock, and the right channel is transmitted on the high cycle. It is typically synchronized to the falling edge of the serial clock, as the data is latched on the rising edge. Dutch manufacturer Van Medevoort has implemented Q-link in some of its equipment, which transfers I²S over four RCA connectors (data, MCK, LRCK, BCK).

See also

References

  • I²S Specification - Philips/NXP
  • I²S and STM32F4 Slides - Auburn University
  • Common inter-IC digital interfaces for audio data transfer,