I²S

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The I²S interface ( Inter-IC Sound ) was developed by Philips for serial digital audio data in communication between ICs . The interface is unidirectional. The clock generation can be carried out by both bus participants.

Overview

The I²S interface is used exclusively for the transmission of digital audio data. These can be present in the form of pulse code modulation (PCM signal) or they can also be coded differently using appropriate control codes. For example, digitally coded data streams according to Dolby E are also transmitted via this interface . With PCM-coded audio signals, two audio channels are always transmitted on the I²S interface, which enables stereo transmission . A data word of the right and left audio channel is alternately transmitted serially. With non-PCM-coded audio transmissions, more than two audio channels can also be transmitted.

An essential property is that this interface is synchronous. Both the source and the sink can generate the clock. The precise timing of the individual sampled audio values ​​is also determined by the existing control lines.

The I²S interface is often used to connect analog-to-digital converters and digital-to-analog converters to digital signal processors (DSP). It is also used as an interface to route audio data to stand-alone digital filter modules .

construction

Timing diagram of the I²S interface

The interface consists of three signal lines, the clock (SCK), data (SD) and word select line (WS). The word select line (WS) defines the exact time frame start and the duration of a serially transmitted data word. In addition, for PCM-coded audio data, it defines, depending on the logic level, whether the audio value currently being transmitted is assigned to the right or left audio channel. The WS line - which is also referred to as word clock - has a frequency that corresponds exactly to the sampling rate .

Communication is only ever in one direction, i.e. H. Audio data are sent, for example, from a DSP to a digital-to-analog converter in order to implement voice output. Another example is that an analog-to-digital converter converts the signals from a microphone into digital values ​​and then sends them to a DSP via an I²S interface.

properties

  • At least three signal lines (SCK, SD, WS), often an additional master clock with 128 to 768 times the sampling rate.
  • No addressing
  • No bidirectional communication
  • Strictly synchronous transmission without pauses between the individual values
  • Combinability of modules with different word lengths

See also

  • I²C (Inter-Integrated Circuit): Another serial data bus developed by Philips Semiconductors.

credentials