44.6.7 Holding Registers

The I2SC user interface includes a Receive Holding Register (RHR) and a Transmit Holding Register (THR). These registers are used to access audio samples for both audio channels.

When a new data word is available in RHR, the Receive Ready bit (RXRDY) in SR is set. Reading RHR clears this bit.

A receive overrun condition occurs if a new data word becomes available before the previous data word has been read from RHR. In this case, the Receive Overrun bit in SR and bit i of the RXORCH field in SR are set, where i is the current receive channel number.

When THR is empty, the Transmit Ready bit (TXRDY) in I2SC_SR is set. Writing to THR clears this bit.

A transmit underrun condition occurs if a new data word needs to be transmitted before it has been written to THR. In this case, the Transmit Underrun (TXUR) bit and bit i of the TXORCH field in SR are set, where i is the current transmit channel number. If the TXSAME bit in MR is ’0’, then a zero data word is transmitted in case of underrun. If MR.TXSAME is ’1’, then the previous data word for the current transmit channel number is transmitted.

Data words are right-justified in RHR and THR. For the 16-bit compact stereo data format, the left sample uses bits 15:0 and the right sample uses bits 31:16 of the same data word. For the 8-bit compact stereo data format, the left sample uses bits 7:0 and the right sample uses bits 15:8 of the same data word.