MAX9217/MAX9218 serializer conciliates one bunch of device chip sets and realizes the data transmiss
MAX9217/MAX9218 serializer conciliates one bunch of device chip sets and realizes the data transmission of the video through a pair of paired line LVDS periodic lines, used in the cars and industry applications extensively. Every frame of the video signal always exists for blanking cycle, can spend these cycles ” bearing the weight of ” Voice data. In note of this application, we discuss the machine format transmission format of the audio frequency, the video link sends the concrete embodiments of machine format method and system implementation. Introduction MAX9217/MAX9218 chip set [1 ] is that a transceiver, to the child, sender (MAX9217) Convert the parallel data to the serial data, send to the receiver (MAX9218) ; The receiver converts the serial data to the parallel data again. This chip set is designed to pass a pair of low-cost twisted pair cables (for instance, commonly used UTP-CAT5 cable in Ethernet) ,Chat on video and the control signal is from the graphics controller (processor) Transmit it to LCD or plasma flat panel display device. The transmission distance can exceed 10 meters. This chip set periodic line is simple in construction, transmission lines used are a low-cost cable, it is expicity ideal schemes of video such as car, instrument, medical equipment,etc.. This chip set not only in order to convey the video signal among bipunctate, sometimes, people still hope it conveys the voice signal at the same time. In note of this application, we will discuss how to utilize blanking interval of the video signal, through controlling the signal channel to convey the voice data to the display unit. We will also explain how to convert the digital voice data to the analog audio signal, and provide the system architecture that the board end loudspeaker of display surface drives. MAX9217/MAX9218 periodic line function and video data form MAX9217 serializer have 27 parallel entry, the speed of bus line is up to 35Mbps. In these 27, 18 are video RGB data: 3 color primarieses take up 6 respectively, other 9 are control signal. The top 3 in 9 control signals is appointed as the vertical, level simultaneously with RGB data: VSYNC(C0) , HSYNC(C1) And ENAB(C2) . 6 control bits left (from C3 to C8) Used in other control signals. In this example, we use a part in 6 control bits to transmit the voice data. MAX9217 can change 18 RGB data or 9 control data into the serial data, then transmit it through LVDS periodic line. Send the control data in the expicity blanking of the video during this period, by RGB data enabling signal (ENAB) Instruction. After MAX9218 receives the serial data, convert it to parallel data the same as MAX9217 input format. Likewise, when MAX9218 outputs the parallel data, according to the sequence regeneration bus line clock in the serial LVDS periodic line. Fig. 1 shows as the video, structure chart controlling the data link to set up and connect between MAX9217 and MAX9218. Fig. 2 shows for the video data and controls machine format sequence. According to video form, sharpness of separation and periodic line speed of display unit, RGB machine format control duty ratio is between 1% and 5%. It pursue 1. video link of MAX9217/MAX9218 structure chart 2. There are many kinds of different forms in video datas and controlling the data pattern of the digital audio of the data format and digital voice data of the transmission format in the serial periodic line. We discuss 3 kinds of most frequently used forms: Sample the digital audio (PCM) , the audio frequency (MP3) of MPEG layer 3 And ATSC digital audio compresses standard (AC3) . PCM digital audio is the data format that CDROM or DVD adopts. Sample and receive PCM digital signal to about voice signal of sound channel, the sampling rate is 44.1kHz, the precision is 16 or 32-bit microcomputer. So, when the precision is 16, PCM audio frequency data rate is 1.41Mbps; The 32-bit microcomputer is 2.42Mbps at. A 700MBCD can be kept 16 music of PCM data format of about 60 minutes. MP3 is the audio frequency form that MP3 player adopts, carry on compressed encoding to PCM voice data. The stereosound MP3 data rate is from 112kbps to 128kbps. As to this kind of data rate, MP3 sound result and CD figure after decoding are audio and identical in quality. AC3 is a figure TV, HDTV and film digital audio code standard. The data rate after the stereosound AC3 code is 192kbps. In order to resume the voice signal,fpvok 5.8G 200mW transmitter for FPV, can send the voice data after encoding into the demoder chip of the audio frequency, this chip produces PCM digital data, convey to the audio frequency DAC, resume into an analog audio signal finally. On the contrary, there are not coded digital voice data that can be sent into the audio frequency DAC directly. (Explain the system implementation of this kind in detail as follows. ) Code or machine format to decode audio frequency daily serial audio frequency digital interface the intersection of Inter-IC and the intersection of audio frequency and the intersection of bus line and (I2S) . Fig. 3 shows for I2S interface disposing and sequential chart. The boundry of each audio frequency word is by the signal WS label. Adopt the Configuration Mode 1 in our application. In the rising edge of SCK signal, the data are latched to the receiver, but when SCK keep the low level, no receive data. Fig. 3. dispose I2S interface and use sequence MAX9217 and periodic line I2S interfaces artificials serial between MAX9218, can convey the voice data to the far-end from one end of the graphics controller. We distribute the control bit C3 and C4 to SD and WS signal respectively. As to SCK clock, if send PCM digital audio, can use MAX9218 convalescent picture element clock PCLK_OUT directly. For conveying MP3 or AC3 audio frequency, can adopt the control bit C5 to produce the picture element clock of half or lower rate for SCK clock. Fig. 4 has revealed the sequence waveforms of these two kinds of situations. In order to prevent the receiver from overflowing, most I2S interface need to carry on metering control, at the serial transmission data, can put SCK low, realize metering control directly. Case1 under 4 Fig., on period SCK unable to put low in signal, can use the intersection of chip selection and pin / CS shut off the receiver. In this case,distribute the Fig. 4 one Case1 to C6 /CS signal. Fig. 4. control data bit blankings undulate of I2S interface than and voice data because voice data are getting more transmissive through blanking cycle of video signal at throughput rate, we need, confirm given the intersection of picture element and the intersection of frequency and fP lay line blanketing than compare with field blanking. Fig. 5 shows for line blanketing and field blanking week on the display panel. Fig. 5. It represent line blanketing with RL line blanketing and field blanking than,show RF field blanking than,let 5 of Fig. show, we can calculate these ratios according to various types of the following: RL =(I1+I2) /L And RF =(f1+f2) /F Therefore receive the throughput rate RA of the voice data, namely: RA =(RFF+(1-RF) RLL) F and L are the audio frequency data transmission utilization factor in blanking cycle among fP. The utilization factor refers to the proportion accounted for in data transmission of audio frequency in the whole blanking cycle, resulted from metering control. As an embodiment, Table 1 illustrated parameter sets up the data rate for the voice data of 3 kinds of types. Table 1. Machine format blanking parameter setting AudioDataTypefPRARBFLDataRate 16 – BitPCMAudioData350.020.0381% 82% 1.41Mbps of different kinds of audio frequency MP317.50.010.0135% 38.5% 128Kbps * AC317.50.010.0150.3% 60% 192Kbps * * note: MP3 and AC3 voice data all contain the head file. Behind information the, actual encoding throughput will slightly higher [2, 3 ]. System implementation want, broadcast voice signal in pieces of board end, we need, send the intersection of audio frequency and or DAC to, decode MP3 and the intersection of AC3 and data the intersection of PCM and data, then send it to audio frequency DAC. Have reverse channel answer, give control device Handshaking signal, the demoder host computer clock must be in pace with picture element clock, in order to prevent the overflow of data or underflow. Systematic structure chart that Fig. 6 shows for the code and the not audio frequency of coded data replays. Fig. 6. Audio frequency of a board end is replayed and realized in the above-mentioned structure chart, has adopted I2S 3 times in the interface. Begin from the left, the first is the same as data rate in the second I2S interface, can reach 35MHz. Third interface – -The interface of MAX9850DirectDrive earphone amplifier [5 ], the fixing of speed is the multiple of the sampling rate of the audio frequency. The clock SCK2 was sent into MAX9491 multi-channel clock generator [6 ], it produced the synchronized clock of demoder, FIFO and MAX9850. MAX9491 offers two programmable PLLs which includes OTP, it is a applied ideal frequency synthesizer. Case1 is suitable for offering and decoding the machine format graphics controller of PCM audio frequency,fpvok 1.2/1.3G The smallest, Case2 is used in the board end of surface and compress machine formatly to decode. The Case1 one metering control from /CS pin realize,at Case2 realize SCK clocks idle. Compare with these two kinds and realize the way, we see PCM audio frequency machine format Case1 does not need to take too much blanking time (Table 1) ,Not needing to use the demoder chip of the audio frequency, the cost is lower than Case2. So, if the graphics controller can produce PCM data from code audio data streams such as MP3 or AC3,etc., propose conveying these data on the periodic line directly. Reference data MAX9217 and MAX9218 data information MPEG audio frequency III frame stucture (Englishonly) The digital audio is compressed (AC-3) (Englishonly) I2S bus line norm (Englishonly) MAX9850 data materials [6 ] MAX9491 are the future products, please contact manufacturer while supplying the state.
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