subject: MAX9217 video link in the transmission of audio data-MAX9217, video link, audio data - Communications Industry [print this page] MAX9217 video link in the transmission of audio data-MAX9217, video link, audio data - Communications Industry
The parallel data into serial data, sent to the receiver (MAX9218); the receiver then the serial data into parallel data.
The circuit design was used by a pair of low-cost twisted pair Cable (Such as Ethernet, commonly used in UTP-cAT5 cable) and control signals from the video graphics controller ( Processor ) Transmitted to LCD Or Plasma Flat Monitor . Transmission distance of more than lOm. The simple circuit group link, use the transmission line for the low-cost cable, automotive, Miriam Table , Medical equipment, the ideal solution for video display. The circuit group can not only transmit video signals between two points, and sometimes, people also want the ability to send audio signals. This article will discuss how to use the video signal blanking control signal through the channel of the audio data to the display.
1 link features and video data formats
MAX9217 serializer with 27-bit parallel input bus rates up to 35Mb / s. In 27, the 18 is the video: RGB data: 3 color of all occupied 6, and the remaining 9 are control signals. 9 control signals in the first three designated as the vertical and horizontal, and RGB data synchronization: VSYNC (c0), HSYNC (c1) and ENAB (C2). The remaining six control bits (c3 to C8) control signals for the other. In this case, we use six control bits in the part of the audio data transmission. MAX9217 can be 18 or 9-bit RGB data is converted to serial data, control data, and then be transmitted via LVDS link their. Blanking period in video display control data sent. From the RGB data enable signal (ENAB) instructions.
MAX9218 serial data is received, it will convert the same with the MAX9217 parallel data input format. Similarly, when the MAX9218 output parallel data, in accordance with the serial LVDS link the timing to re-generate the bus clock. Figure l shows the MAX9217 and MAX9218 between the video and control data link setup and connection in the process.
2 digital audio data types and transmission formats
Digital audio data, a number of different formats. 3 The most commonly used digital audio format is sampled ( PCM ), MPEG Layer 3 audio ( MP3 ) And ATSC digital audio compression standards (AC3). PCM digital audio is a CD ROM or DVD Data format used. On the left and right channel audio signal sampled PCM digital signal, sampling rate of 44. lkHz, precision 16-bit or 32-bit. Therefore, the precision is 16 bits, PCM audio data rate of 1.41Mb / s; 32 bits to 2.42Mb / s. 1 700MBCD save about 60 minutes of 16-bit PCM data format of music.
MP3 is a MP3 player, audio format used on PCM audio data compression. Stereo MP3 data rate of 112kb / s to 128kb / s. For this data rate, the decoded MP3 digital audio sound quality with the same CD. AC3 digital TV, HDTV and Film Digital audio coding standard. Stereo AC3 encoded data rate is 192kb / s.
Order to restore the audio signal can be encoded audio data into audio Decoder The decoder generates PCM digital data, sent to the audio DAC, eventually revert back to analog audio signals. On the contrary, there is no coding of digital audio data directly into the audio DAC. Encoding or decoding audio data commonly used serial digital audio interface is Inter? IC Audio bus (12S). Figure 2 shows the 12S interface configuration and timing diagram. The boundary of each word from the audio signal WS Logo . Used in our application configuration mode l. The rising edge of the SCK signal, data is latched to the receiver, but when SCK is held low when not receiving data.
Use the MAX9217 and MAX9218 serial link between the simulation 12S interface, audio data can be transmitted from the graphics controller to the remote end. We will control bits C3 and C4 were assigned to the SD and WS signal. The SCK clock, if you want to send the PCM digital audio, you can directly use the MAX9218 to restore the pixel clock PCLK-0UT. For the transfer MP3 or AC3 audio, can be used as the control bit SCK Clock Generation C5 or lower half of the pixel clock rate. Figure 3 shows the situation of these two timing waveforms. To prevent receiver overflow, most of the IX3 interfaces need to throttle control and continuously send data, you can set SCK low, the direct realization of throttle control. Figure 3 in case 1, the work can not be set low during the SCK signal, you can use the chip select pin GS closed receiver. In this case, the CS signal assigned to C6.
3 system implementation To Panel End Play audio signal needs to be sent to the audio DAC PCM data or decode MP3 and AC3 data, and then sent to the audio DAC. In the absence of the reverse channel will be sent to the controller handshake signals back to the decoder master clock must be synchronized with the pixel clock to prevent data overflow or underflow. Figure 4 shows the data encoding and not encoding audio replay of the system structure.
Map, using 3 12S interfaces. From the left, the first and second identical 12S interface data rate, can reach 35MHz. The third interfaces?? MAX9850DirectDfive Headset Amplifiers Interface, fixed rate Audio sample Rate multiple. MAX9491 clock into multiple clock SCK2 Generator , It generates decoder, FIFO, and MAX9850's synchronous clock. MAX9491 provides Package With OTP's two programmable PLL, is ideal for this application, the frequency synthesizer. Case 1 applies to decode the PCM audio data to provide the graphics controller, case 2 panel side for decoding the compressed data. For case 1 the throttle control to achieve by the CS pin, 2 types of circumstances to achieve through the idle clock SCK. Comparison of these two implementations, we see the data PCM audio case 1 does not require much of the blanking time (Table 1), do not use the audio decoder circuitry, cost less than the case 2. Therefore, if the graphics controller, etc. from MP3 or AC3 encoded audio data to generate PCM data stream, the proposed direct transmission of the data in the link. [Key words]: MAX9217 Video Link Audio data Comment Large In Small
