#ps321

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Author: Electronic research and development centre of Limited Company of overseas Chinese of Xiamen Wang ZhengYu With the increase of the consumption electronic functional requirement, it is applied to the consumption electronic product that HDMI is increasingly much as the video interface of new monobasic digital sound. Electronic products with HDMI function come out in a large amount, the interface quantity of HDMI thereupon increases too. As one carrier that audio frequency and video display, the intersection of HDMI and mainly as digital the intersection of audio frequency and video and machine format receiving end application of interface its digital television. In order to make the digital television connect more HDMI apparatuses, a lot of integrated circuit design companies have put out and selected one or four HDMI switches to select one three times in right time, used for meeting many interface of HDMI receiving end's demands. This text three on the basis of one of Parade Company of main introduction selects the application of HDMI switch PS321 to be designed. Hardware design A chip lectotype PS321 has the advantage of being more compared with similar products of other manufacturers as a section of three HDMI switches to select one. Select HDMI switch to carry on comparison PS321 and general three for another one, the result is shown in Table 1. Can find out PS321 has the advantage of being following more than the centering from the above. In data transmission rate, the intersection of HDMI and the intersection of line and transmission distance, energy-conservation and ESD ' Anti-electrostatic) The respect has advantages; Support I2C to control, help the artificer use; Built-in EDID buffers, needn't be on HDMI interface and E2PROM used for storing EDID data, thus reduce the cost of circuit; Built-in equalizer, the gain to noise temperature ratio of the adjustable, the transmission losses used for remedying HDMI signal on the circuit. 2 circuit design DDC interface circuit design DDC (reveal the communications link) Used mainly in HDMI source end apparatus (Source) With the receiving end apparatus (Sink) Between carry on EDID data and HDCP cipher key exchange. Exchange through EDID, the source end apparatus can know the receiving capability of the apparatus audio frequency and video of receiving end; Through exchange of HDCP Key, can real time content to go on data flow protect and authorize, thus achieve the goal that the data content protects. The circuit way of DDC is the same as I2C circuit, so in DDC circuit design, artificers should consider DDC level of circuits. According to HDMI 1.3a norm, HDMI source end DDC 1.5kΩ, consider the intersection of HDMI and the intersection of DDC and requirement of level (between 4.5- 5.5V) authorize, ,Pull DDC signal to the 18th pin (HDMI source end 5V power) of HDMI interface on the resistance through 10kΩ,. Through calculating, the minimum that DDC of source end and receiving end always pulls upward the resistance is always pulled upward min for R =1.5kΩ| 10kΩ=1.3kΩ. Through testing, the level of the receiving end DDC is about 4.68V, so meet HDMI and authorize the requirement; Norm that the minimum value 1.3kΩ that and DDC always pulls upward the resistance met I2C. Fig. 1 DDC interface circuit diagram Because pull weakly upward DDC of PS321, , at the apparatus, pulling level upward, can transmit the intersection of HDMI and the 18th pin of interface to through resistance of 10kΩ inside the DDC as the intersection of HDMI and the intersection of interface and unreceived the intersection of HDMI and source, cause the 18th pin level of HDMI interface to be greater than 1.5V, is unsatisfied with HDMI and authorize the requirement. Need, connect, reach place by one resistance of 3.6kΩ the intersection of HDMI and pin this of interface. Through testing, as the unreceived HDMI source apparatus of HDMI interface, the 18th pin level of HDMI interface is about 0.5V, meet HDMI and authorize the requirement. The equalizer is designed It is for the weak signal to do essential signal shaping that the equalizer is designed, in order to guarantee the transmissive completeness of HDMI data. Under I2C operating mode, can set up the magnitude of gain to noise temperature ratio of the equalizer by register. The magnitude of gain to noise temperature ratio of oral equalizer of 3 HDMI input terminuses can be regulated separately, as shown in Table 2. Where to block the artificer can decide by loss of the 3 HDMI input port signals one to adopt. Test as follows: Prepare two HDMI threads, a long 5m, a long 10m, transmits the signal of 2.25Gb/s data rate too under the circumstances that the gain to noise temperature ratio of the equalizer is the default value, data eye pattern got. Through comparison, the area of 10m long transmission eye pattern is smaller than that of 5m, but does not influence the completeness of the transmission signal. The artificer needs to judge a gain to noise temperature ratio blocked that which the power of the signal is in order to determine to adopt while using the equalizer to design. Often meet a side HDMI interface of need in the TV design at present, and the intersection of HDMI and switch at mother board, have the intersection of segment and distance from side the intersection of HDMI and interface usually. Certainly this distance will seldom exceed 1m, adopting the canonial HDMI thread will not influence signal quality, but if adopting the ordinary lunk may cause the signal distortion. Need through the appropriate magnitude of gain to noise temperature ratio of improving the equalizer at this moment, in order to guarantee the transmissive completeness of signal. . The collinear transmission signal of ordinary connection gathered for PS321 input end on left side, can see the area of eye pattern is waned, the losses of the signal are very great; The right side is a transmission signal gathered after improving the gain to noise temperature ratio of the equalizer through PS321, can see the signal resumes completeness after facelift. Transmission eye pattern of Fig. 2 2.25Gb/s data rate Fig. 3 improves the gain to noise temperature ratio of the equalizer in order to guarantee the transmissive completeness of signal PCB of TMDS signal designs HDMI data flow transmitted in the form of TMDS signal, includes three pairs of differentiating data link and a pair of differentiating clock line. According to HDMI 1.3a norm, require TMDS differentiating impedance to be 100Ω± 15%. If design according to two floors of PCB. Through calculating, the thickness of two layers of PCB is 61.2+ 1.9 + 1.9= 65Mil, about 1.6mm; The dielectric constant of PCB planking is 4.2. Require for goal of 100Ω, bring the intersection of differentiating and impedance into, calculate parameter the above software calculate in the Polar Si9000 according to the intersection of TMDS and the intersection of differentiating and impedance, will get the guidance parameter that PCB will be designed. Double-deck PCB framework of Fig. 4 The differentiating impedance of Fig. 5 is calculated Can obtain the following PCB design parameters from Fig. 5: It is 12.5mil that the line width leaves in the differentiating; The parting-line interval of difference is 5mil; Impedance about 100Ω of the differentiating. Software design 1 HPD operation designed HPD (Hotplug heat plugged) Operate and design an important link that is HDMI interface software design, it is by the receiving end apparatus (Sink) The one that send out is here with HDMI source end apparatus (Source) Between prelude signal if you can't set up formally, communicated. Show the receiving end apparatus has been already ready when HPD signal level is for being high, allow the source end apparatus to visit the receiving end apparatus. In the software design of HPD operation, should consider the following two factors. First, the power foot (the 18th pin of HDMI receiving end socket) that HDMI source end apparatus exports Detection. If the 18th pin of HDMI receiving end socket is the low level, show HDMI source end apparatus is not ready, the receiving end at this moment apparatus should put HPD signal the low level; If the 18th pin of HDMI receiving end socket is the high level, show HDMI source end apparatus has been already ready, the receiving end at this moment apparatus there can be the one that chose to put HPD signal the high level according to the autogenous situation, with the notice HDMI source end apparatus, it is ready to show the receiving end apparatus too. Second, source end and simulation HPD operation under of communicating and failing of receiving end. May when HDMI source end and communication of the receiving end were just set up present HDCP-KEY and read failing or EDID data and read the Improper situation, lead to the fact HDMI to work abnormally, in order to resume normal communication, need to carry on analog HPD operation at this moment, namely is drawn HPD signal as the low level from the high level by the receiving end apparatus, HPD low level lasting about 100ms, retract high level and then, source end apparatus will measure the intersection of HPD and jump transfer of signal in this way, initiate and read the fetch operation again, do the further attempt for setting up normal communication. The software simulation can in need artificial heat plug under the assistance that operate coming the intersection of rebuild and normal communication of HDMI by the intersection of simulation and hard way that plug in operation of HPD, thus can dispel the unstable trouble that causes of communication. In view of the above-mentioned two factors, artificers can know the software design procedure of HPD operation very easily, . Software design procedure of Fig. 6 HPD operation 2 CEC operation designed CEC (consumption electronic control) Operation is an important expanded function of HDMI interface, it adopts " first line " ( One Wire) Communication mode, connect the apparatus of HDMI, make the operation between HDMI apparatus simplify. If PS321 disposes by buffering area of Built-in: EDID, then CEC operation of PS321 is designed is mainly the distribution of CEC physical address, . Fig. 7 CEC physical address allocation The distribution of CEC physical address has two ways: Hardware way and software way. Hardware way After HDMI receiving end apparatus power up, the system includes EDID data EDID of the physical address write PS321 of HDMI port 1 through I2C The buffering area, the oral physical address allocation of 3 ends of HDMI is as follows: The acquiescence of the port 1 is 1.0.0.0; The physical addresses of the port 2 and port 3 are by PS321 Realize on the basis of default address of the port 1 by way of hardware " Add by one automatically " Operate and get, so the port 2 is 2.0.0.0; The port 3 is 3.0.0.0. The acquired CEC physical address is stationary by way of hardware, can't change, so the physical addresses of the HDMI port 2 and port 3 can not change. The hardware way sets up the procedure of CEC physical address. Fig. 8 hardware way sets up the flow block diagram of CEC physical address Software way The physical address of HDMI port 1 comes from EDID buffering area, include the intersection of HDMI and the intersection of port and 1 physical the intersection of address write and EDID buffering area of PS321 by system the intersection of EDID and data through I2C, this is the same as hardware way. HDMI the intersection of port and 2 - 3 physical address store specialized register in, adjust, take, map their to EDID buffering area. CEC physical address set up by way of software can be changed. Software way sets up the reference procedure code of CEC physical address as follows: Set HPD Low //Set HPD signal as the low level WriteREG(Page0.0x10,0x01) //Activate software way and set up CEC physical address Load EDID to PS321 EDID Buffer for HDMI1 //The physical address write EDID buffering area of EDID data including HDMI port 1 Load CEC Physical Address location to Page0.0x17 //The position load register 0x17 of CEC physical address Load CEC Physical Address&checksum for HDMI2 to Page0.0x11- 0x13 //HDMI2 physical address and register 0x11 of one yard of loads of check-up- 0x13 Load CEC Physical Address&checksum for HDMI3 to Page0.0x14- 0x16 //HDMI3 physical address and register 0x14 of one yard of loads of check-up- 0x16 WriteREG(Page0.0x10,0x07) //It has been already ready that 3 HDMIs carried the physical address of oral EDID and CEC Set HPD High //Set HPD signal as the high level Conclusion Design application on PS321,can understanding HDMI switch further design main point in soft hardware design. With a large number of use of HDMI interface and development of data flow of audio frequency and video of high definition, HDMI switch will develop and integrate more, newer function application, for example, TMDS signal adaptive equalization function; Such functions as HDMI-CEC order is received, decoded and sent. http://www.epc.com.cn/magzine/20081212/12020.asp