SDAA014 November   2025 AM2752-Q1 , AM2754-Q1

 

  1.   1
  2.   Abstract
  3.   How to Use this Document
  4.   Trademarks
  5. 1Digital Audio Formats
    1. 1.1 I2S
    2. 1.2 TDM
  6. 2McASP Overview
  7. 3McASP Connections for AM275x
    1. 3.1 McASP Common Configurations
      1. 3.1.1 McASP as a Clock Controller
        1. 3.1.1.1 Clocks Generated using the Internal Audio PLL
        2. 3.1.1.2 Clocks Generated using the AUDIO_EXT_REFCLK AUXCLK Source
        3. 3.1.1.3 Clocks Generated using the AUDIO_EXT_REFCLK AHCLK Source
      2. 3.1.2 McASP as Clock Peripheral
        1. 3.1.2.1 Clock Externally Generated with AUDIO_EXT_REFCLK Input
  8. 4McASP Layout Considerations
    1. 4.1 McASP Signals Shared with Bootmode Logic
    2. 4.2 McASP Topology for Multiple Devices in Single Clock Domain
  9. 5ASRC Overview
  10. 6McASP Practical Examples
    1. 6.1 Audio Playback with Internal Audio PLL for Two Clock Domains
    2. 6.2 Audio Playback with External Clock Source and McASP SYNC mode
    3. 6.3 Audio Playback with ASRC Bridging Two Clock Domains
  11. 7Key Audio System Design Takeaways
  12. 8References

1 Digital Audio Formats

Digital audio data is communicated through 3-wire formats. The three signals required for audio transmission are bit clock, frame sync, and serial audio data. Multiple audio slots are contained within a frame of data. Audio channels are assigned to unique slots to send multichannel audio over a single bus. A single audio data frame contains a single samples for each channel being transferred. The various digital audio formats will define how the frame of audio data is organized and transferred between devices. In general, all audio frame formats are defined by the following characteristics:

  • Falling or rising edge of frame sync indicates frame start
  • Delay between frame sync edge and data transmission
  • Frame sync width
  • Number of unique audio channels per frame
  • Slot size in bits per channel
  • Word depth in bits per slot
  • Bitstream order (MSB or LSB first)
  • Bit clock polarity for sampling audio data
    Note: There are many generic names for the signals of digital audio. Frame sync (FS) may also be referred to as LRCLK, WCLK, or Word Select. Bit clock may also be referred to as serial clock or audio clock. In this document, the standard naming of frame sync and bit clock is used.

Slots of audio may have words that are less than the total slot bit width. When the word depth is smaller than the slot size, then the word can be aligned to the left of the slot or the right of the slot. Because of different alignment options, it is important to have a complete understanding of how the bits are being padded to interpret the audio data.

Figure 1-1 shows an example audio slot that has a most significant bit first serial bitstream, 24-bit word depth (left-aligned), and 32-bit slot size.

Bit, Word, and Slot in a Frame Figure 1-1 Bit, Word, and Slot in a Frame