User Manual

element14 is a trademark of Premier Farnell plc 70

6.10.6 Audio Interface

There is an I2S audio interface between the processor and the

TDA19988

. Stereo audio

can be transported over the HDMI interface to an audio equipped display. In order to

create the required clock frequencies, and external 24.576MHz oscillator,

, is used.

From this clock, the processor generates the required clock frequencies for the

TDA19988

There are three signals used to pass data from the processor to the

TDA19988

. SCLK is

the serial clock. SPI1_CS0 is the data pin to the

TDA199888

. SPI1_D0 is the word sync

pin. These signals are configured as I2S interfaces.

Audio is limited to CEA supported resolutions. LCD panels only activate the audio in

CEA modes. This is a function of the specification and is not something that can be fixed

on the board via a hardware change or a software change.

In order to create the correct clock frequencies, we had to add an external

24.576MHZ

oscillator. Unfortunately this had to be input into the processor using the pin previously

used for

GPIO3_21

. In order to keep GPIO3_21 functionality, we provided a way to

disable the oscillator if the need was there to use the pin on the expansion header.

Figure

shows the oscillator circuitry.

Figure 45 24.576MHz Oscillator