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

4.1 McASP Signals Shared with Bootmode Logic

The AM275x has 16 bootmode signals that are used by the ROM to determine which peripheral is being used for boot and other boot configuration parameters. The 16 bootmode signals are tied to a specific pad of the SoC, and the AM275x uses most of the McASP0 interface pads for the bootmode pads.

Each bootmode pad requires an external pull up or pull down resistor to define a digital logic high or low state for the associated bootmode signal during the power up sequence.

Because the McASP0 signals are shared with the bootmode logic, it is very important to review and ensure the following:

  • The audio device connected to the McASP0 interface does not have the ability to drive on the bootmode signals during the initial power up or in the event of a reset. For example, if PORz is asserted for the AM275x, then the McASP0 audio device should be held in reset as well until the boot sequence is completed.
    • An external driver on the bootmode logic during power up or reset will lead to unpredictable bootmode states.
  • The external pull resistors should be placed in line with the signal trace such that they do not introduce a stub. Figure 4-1 shows examples of pull resistors with and without trace stubs, where the green implementation should be replicated for designs.
    • Stubs on the signal traces, especially on the bit clock, will impact the reliability of the audio data as signal reflections caused by the stub can lead to timing errors and signal distortion.

McASP Signal Trace Stubs Figure 4-1 McASP Signal Trace Stubs