The FPGA contains an ARM PrimeCell Advanced Audio CODEC Interface (AACI) that provides communication with a CODEC using the AC-link protocol. This section provides a brief overview of the AACI. For detailed information, see PrimeCell Advanced Audio CODEC Interface (PL041) Technical Reference Manual.
For a description of the audio CODEC signals, refer to the LM4549 datasheet available from the National Semiconductor website.
The AACI on the Versatile/AB926EJ-S connects to a National Semiconductor LM4549 audio CODEC. The audio CODEC is compatible with AC’97 Rev 2.1. Table 3.6 lists the specifications for the audio system.
|Raw digital audio data format||PCM|
|Number of audio channels|
Out 2 (stereo)
In 1 of 2 (mono)
|Audio sample data width||12, 16 or 18-bit native. Other data sizes require software conversion of sample data.|
|Sample rates supported||4kHz to 48kHz, variable in 1Hz steps. Record and playback sample rates can be independently selected.|
|Audio power output||250mWRMS into 32Ω|
Figure 3.18 shows the architecture of audio interface.
Two microphone inputs are present on J3. Only monophonic sound is supported, but microphone channel CODEC_MIC1 or CODEC_MIC2 can be selected in software. Solder link LK1 selects passive or active (electret) microphones:
- Link AB
Active microphone with power on CODEC_MIC1 (tip). Passive microphone on CODEC_MIC2 (not powered).
This is the default configuration.
- Link BC
Active microphone with power on CODEC_MIC2 (ring). Passive microphone on CODEC_MIC1 (not powered).
- No link
Passive microphone on CODEC_MIC1 and CODEC_MIC2.