The standard I²S protocol is defined for only two channels: left and right. In I²S mode, the MSB of the left slot 0 is transmitted on the falling edge of BCLK in the second cycle after the falling edge of FSYNC. The MSB of the right slot 0 is transmitted on the falling edge of BCLK in the second cycle after the rising edge of FSYNC. Each subsequent data bit is transmitted on the falling edge of BCLK. In master mode, FSYNC is transmitted on the rising edge of BCLK. Figure 8-5 and Figure 8-6 show the protocol timing for I²S operation in slave and master mode of operation.

Figure 8-5 I²S Mode Protocol Timing in Slave Mode

Figure 8-6 I²S Protocol Timing In Master Mode

For proper operation of the audio bus in I²S mode, the number of bit clocks per frame must be greater than or equal to the number of active output channels (including left and right slots) times the 32-bits word length of the output channel data. The device FSYNC low pulse must be a number of BCLK cycles wide that is greater than or equal to the number of active left slots times the 32-bits data word length. Similarly, the FSYNC high pulse must be a number of BCLK cycles wide that is greater than or equal to the number of active right slots times the 32-bits data word length. The device transmit zero data value on SDOUT for the extra unused bit clock cycles.