Using the 24-bit Audio CODEC

The DE2 board provides high-quality 24-bit audio via the Wolfson WM8731 audio CODEC (enCOder/DECoder). This chip supports microphone-in, line-in, and line-out ports, with a sample rate adjustable from 8 kHz to 96 kHz. The WM8731 is controlled by a serial I2C bus interface, which is connected to pins on the Cyclone II FPGA. A schematic diagram of the audio circuitry is shown in Figure 1, and the FPGA pin assignments are listed in Table 1. Detailed information for using the WM8731 codec is available in its datasheet.

Table 1. Audio CODEC signal assignments

Signal NameDescription
AUD_ADCLRCK Audio CODEC ADC LR Clock
AUD_ADCDAT Audio CODEC ADC Data
AUD_DACLRCK Audio CODEC DAC LR Clock
AUD_DACDAT Audio CODEC DAC Data
AUD_XCK Audio CODEC Chip Clock
AUD_BCLK Audio CODEC Bit-Stream Clock
I2C_SCLKI2C Data
I2C_SDAT I2C Clock

See DE2_pin_assignments.csv, a comma-delimited file that matches "standard" descriptive names to actual FPGA pin locations. This file can be directly opened in Microsoft Excel.

Manufacturer's Description

The WM8731 is a low-power stereo CODEC with an integrated headphone driver, designed specifically for portable MP3 audio and speech players and recorders.

Stereo, line and mono microphone level audio inputs are provided, along with a mute function, programmable line level volume control and a bias voltage output suitable for an electret type microphone.

The device is controlled via a 2 or 3 wire serial interface. The interface provides access to all features, including volume control, mutes, de-emphasis, and power management facilities.

References

   WM8731/WM8731L Portable Internet Audio CODEC with Headphone Driver and Programmable Sample Rates, datasheet

   DE2 User Manual, version 1.4, 2006. (pdf)


Maintained by John Loomis, last updated 18 April 2007