In Master and Controller modes, the I2S provides the Serial Clock, a Word Select/Frame Sync signal and optionally a Master Clock.
In Controller mode, the I2S Serializers are disabled. Only the clocks are enabled and output for external receivers and/or transmitters.
In Slave mode, the I2S receives the Serial Clock and the Word Select/Frame Sync Signal from an external master. SCKn and FSn pins are inputs.