beaglebone-black - Flipbook - Page 62
BeagleBone Black
6.6.4 HDMI Control Processor Interface
In order to use the TDA19988, the processor needs to setup the device. This is done via the I2C interface
between the processor and the TDA19988. There are two signals on the TDA19988 that could be used to set
the address of the TDA19988. In this design they are both tied low. The I2C interface supports both 400kHz
and 100KhZ operation. Table 10 shows the I2C address.
Fig. 6.27: TDA19988 I2C Address
6.6.5 Interrupt Signal
There is a HDMI_INT signal that connects from the TDA19988 to the processor. This signal can be used to alert
the processor in a state change on the HDMI interface.
6.6.6 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, an external
24.576MHz oscillator,*Y4*, 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 con昀椀gured 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 speci昀椀cation and is not something that can be 昀椀xed 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 45 shows the oscillator circuitry.
Fig. 6.28: 24.576MHZ Oscillator
6.6. HDMI Interface
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