9.3.6 Digital Audio IO Interface

Audio data flows between the host processor and the TLV320AIC3204 on the digital audio data serial interface, or audio bus. This very flexible bus includes 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 TLV320AIC3204 can be configured for left or right-justified, I²S, DSP, or TDM modes of operation, where communication with standard telephony 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 maximum of the selected ADC and DAC sampling frequencies.

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, and to support the case when multiple TLV320AIC3204s may share the same audio bus.

The TLV320AIC3204 also includes a feature to offset the position of start of data transfer with respect to the word-clock. Control the offset in terms of number of bit-clocks by programming Page 0, Register 28.

The TLV320AIC3204 also has the feature to invert the polarity of the bit-clock used to transfer the audio data as compared to the default clock polarity used. This feature can be used independently of the mode of audio interface chosen. Page 0, Register 29, D(3) configures bit clock polarity.

The TLV320AIC3204 further includes programmability (Page 0, Register 27, D(0)) to place the DOUT line into a hi-Z (3-state) condition during all bit clocks when valid data is not being sent. By combining this capability with the ability to program at what bit clock in a frame the audio data begins, time-division multiplexing (TDM) can be accomplished, enabling the use of multiple codecs on a single audio serial data 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 TLV320AIC3204, these clocks are active only when the codec (ADC, DAC or both) are powered up within the device. This intermittent clock operation reduces power consumption. However, it also supports a feature when both the word clocks and bit-clocks can be active even when the codec in the device is powered down. This continuous clock feature 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.