7.3.6 Digital Audio I/O Interface

Audio data is transferred between the host processor and the TLV320DAC3203 via the digital audio data serial interface, or audio bus. The audio bus on this device is very flexible, including left or right-justified data options, support for I²S or PCM protocols, programmable data length options, a TDM mode for multichannel operation, very flexible master/slave configurability for each bus clock line, and the ability to communicate with multiple devices within a system directly.

The audio bus of the TLV320DAC3203 can be configured for left or right-justified, I²S, DSP, or TDM modes of operation, where communication with standard PCM interfaces is supported within the TDM mode. These modes are all MSB-first, with data width programmable as 16, 20, 24, or 32 bits by configuring Page 0, Register 27, D(5:4). In addition, the word clock and bit clock can be independently configured in either Master or Slave mode, for flexible connectivity to a wide variety of processors. The word clock is used to define the beginning of a frame, and may be programmed as either a pulse or a square-wave signal. The frequency of this clock corresponds to the DAC sampling frequency.

The bit clock is used to clock in and clock out the digital audio data across the serial bus. When in Master mode, this signal can be programmed to generate variable clock pulses by controlling the bit-clock divider in Page 0, Register 30. The number of bit-clock pulses in a frame may need adjustment to accommodate various word-lengths as well as to support the case when multiple TLV320DAC3203s may share the same audio bus.

The TLV320DAC3203 also includes a feature to offset the position of start of data transfer with respect to the word-clock. This offset can be controlled in terms of number of bit-clocks and can be programmed in Page 0, Register 28.

The TLV320DAC3203 also has the feature of inverting the polarity of the bit-clock used for transferring the audio data as compared to the default clock polarity used. This feature can be used independently of the mode of audio interface chosen. This can be configured via Page 0, Register 29, D(3).

The TLV320DAC3203 includes the programmability to program at what bit clock in a frame does audio data begin. This enables time-division multiplexing (TDM), enabling use of multiple codecs on a single audio bus. When the audio serial data bus is powered down while configured in master mode, the pins associated with the interface are put into a hi-Z output condition.

By default when the word-clocks and bit-clocks are generated by the TLV320DAC3203, these clocks are active only when the DAC is powered up within the device. This is done to save power. However, it also supports a feature when both the word clocks and bit-clocks can be active even when the DAC in the device is powered down. This is useful when using the TDM mode with multiple codecs on the same bus, or when word-clock or bit-clocks are used in the system as general-purpose clocks.