3.7. Advanced Audio CODEC Interface, AACI

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.

The AACI in the baseboard FPGA can be disabled and the signals driven by an AACI implemented in the FPGA of an attached Logic Tile in tile site 1 or 2.


For a description of the audio CODEC signals, refer to the LM4549 data sheet available from the National Semiconductor web site. See also Advanced Audio CODEC Interface, AACI.

The AACI on the baseboard connects to a National Semiconductor LM4549 audio CODEC. The audio CODEC is compatible with AC’97 Rev 2.1. Table 3.8 lists the specifications for the audio system.

Table 3.8. Audio system specification

Raw digital audio data formatPCM
Number of audio channels

Out 2 (stereo)

In 1 of 2 (mono)

Audio sample data width12, 16 or 18-bit native. Other data sizes require software conversion of sample data.
Sample rates supported4kHz to 48kHz, variable in 1Hz steps. Record and playback sample rates can be independently selected.
Audio power output250mW RMS into 32Ω

Figure 3.25 shows the architecture of audio interface.

Figure 3.25. Audio interface

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Two microphone inputs are present on J4. 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.

The signals associated with the audio CODEC interface are also assigned to connector J43, the AACI expansion socket pins, as shown in Table 3.9.


The AACI expansion connector J45 is not fitted to the baseboard.

Table 3.9. AC’97 audio debug signals on J3

Pin numberSignal nameDescription
1AACIBITCLKClock from the CODEC to the AACI
2AACISYNCFrame synchronization signal from the AACI
3AACISDATAINSerial data from the CODEC to the AACI
4AACI_RESETReset signal from the AACI to the CODEC
5AACISDATAOUTSerial data from the AACI to the CODEC
6GNDSignal ground

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