Many digital audio systems are being introduced into the consumer audio market, including compact disc, digital audio tape, digital sound processors, and digital TV-sound. The digital audio signals in these systems are being processed by a number of (V)LSI ICs, such as:
• A/D and D/A converters;
• digital signal processors;
• error correction for compact disc and digital recording; • digital filters;
• digital input/output interfaces.
Standardized communication structures are vital for both the equipment and the IC manufacturer, because they increase system flexibility. To this end, we have developed the inter-IC sound (I2S) bus – a serial link especially for digital audio.
2.0 BASIC SERIAL BUS REQUIREMENTS
The bus has only to handle audio data, while the other signals, such as sub-coding and control, are transferred separately. To minimize the number of pins required and to keep wiring simple, a 3-line serial bus is used consisting of a line for two time-multiplexed data channels, a word select line and a clock line.
Since the transmitter and receiver have the same clock signal for data transmission, the transmitter as the master, has to generate the bit clock, word-select signal and data. In complex systems however, there may be several transmitters and receivers, which makes it difficult to define the master. In such systems, there is usually a system master controlling digital audio data-flow between the various ICs. Transmitters then, have to generate data under the control of an external clock, and so act as a slave. Figure 1 illustrates some simple system configurations and the basic interface timing. Note that the system master can be combined with a transmitter or receiver, and it may be enabled or disabled under software control or by pin programming.