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ITU-R_BT.656协议

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ITU-R_BT.656协议

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RECOMMENDATION ITU-R BT.656-5 Interface for digital component video signals in 525-line and 625-line television systems operating at the 4:2:2 level of Recommendation ITU-R BT.601* (Question ITU-R 42/6) (1986-1992-1994-1995-1998-2007) Scope This Recommendation covers the data structure of the parallel signal representation and serial interface for 525/625-line digital signals as defined in Recommendation ITU-R BT.601. The ITU Radiocommunication Assembly, considering a) that there are clear advantages for television broadcasting organizations and programme producers in digital studio standards which have the greatest number of significant parameter values common to 525-line and 625-line systems; b) that a worldwide compatible digital approach will permit the development of equipment with many common features, permit operating economies and facilitate the international exchange of programmes; c) that to implement the above objectives, agreement has been reached on the fundamental encoding parameters of digital television for studios in the form of Recommendation ITU‑R BT.601; d) that the practical implementation of Recommendation ITU-R BT.601 requires definition of details of interfaces and the data streams traversing them; e) that such an interface should have a maximum of commonality between 525-line and 625-line versions; f) that in the practical implementation of Recommendation ITU-R BT.601 it is desirable that a bit-serial interface be defined, recommends 1 that where an interface is required for component-coded digital video signals described in Recommendation ITU‑R BT.601 in television studios, the interface and the data streams that will traverse them should be in accordance with Annex 1, defining the bit-serial implementation. Annex 1 1 Introduction This Recommendation describes the means of interconnecting digital television equipment operating on the 525-line or 625-line standards and complying with the 4:2:2 encoding parameters as defined in Recommendation ITU-R BT.601. Part 1 describes the digital signal format of the interface. Part 2 describes the particular characteristics of the bit-serial interface. The particular characteristics of the bit-parallel interface are to be found in Appendix 1. PART 1 Digital signal format of the interface 1 General description of the interface The interface provides a unidirectional interconnection between a single source and a single destination. (NOTE – With the use of signal routers the destination may be multiple destinations.) A digital signal format of the interface is described in § 2. The data signals are in the form of binary information coded in 8- or 10-bit words (see Note 1). These signals are: – video signals, – digital blanking data, – timing reference signals, – ancillary signals. NOTE 1 – Within this Recommendation, the contents of digital words are expressed in hexadecimal form of 10-bit representation. For example, the bit pattern 1001000101 is expressed as 245h. Eight-bit words occupy the left most significant bits of a 10-bit word, i.e. bit 9 to bit 2, where bit 9 is the most significant bit. 2 Video data 2.1 Coding characteristics The video data is in compliance with Recommendation ITU-R BT.601, and with the field‑blanking definition shown in Table 1. TABLE 1 Field interval definitions 2.2 Video data format The data words in which the eight most significant bits are all set to 1 or are all set to 0 are reserved for data identification purposes and consequently only 254 of the possible 256 8-bit words or 1 016 of the possible 1 024 10-bit words may be used to express a signal value. The video data words are conveyed as a 27 Mword/s multiplex in the following order: CB, Y, CR, Y, CB, Y, CR, etc. where the word sequence CB, Y, CR, refers to co-sited luminance and colour-difference samples and the following word, Y, corresponds to the next luminance sample. 2.3 Interface signal structure Figure 1 shows the ways in which the video sample data is incorporated in the interface data stream. Sample identification in Fig. 1 is in accordance with the identification in Recommendation ITU‑R BT.601. 2.4 Video timing reference codes (SAV, EAV) There are two timing reference signals, one at the beginning of each video data block (start of active video, SAV) and one at the end of each video data block (end of active video, EAV) as shown in Fig. 1. Each timing reference signal consists of a four word sequence in the following format: 3FF 000 000 XYZ. (Values are expressed in hexadecimal notation. 3FF 000 values are reserved for use in timing reference signals.) The first three words are a fixed preamble. The fourth word contains information defining field 2 identification, the state of field blanking, and the state of line blanking. The assignment of bits within the timing reference signal is shown in Table 2. TABLE 2 Video timing reference codes Bits P0, P1, P2, P3, have states dependent on the states of the bits F, V and H as shown in Table 3. At the receiver this arrangement permits one-bit errors to be corrected and two-bit errors to be detected. TABLE 3 Protection bits 2.5 Ancillary data The ancillary signals should comply with Recommendation ITU-R BT.1364. 2.6 Data words during blanking The data words occurring during digital blanking intervals that are not used for the timing reference code or for ancillary data are filled with the sequence 200h, 040h, 200h, 040h etc. corresponding to the blanking level of the CB, Y, CR, Y signals respectively, appropriately placed in the multiplexed data. PART 2 Bit-serial interface 1 General description of the interface A serial interface is an interface in which the bits of a data word, and successive data words, are sent consecutively via a single transmission channel. The serial interface is capable of carrying video, audio, and ancillary data. It may also be used for carrying packetized data in accordance with Recommendation ITU-R BT.1364. The transmission of signals can be achieved in both electrical form, using coaxial cable, and in optical form using an optical fibre. Coaxial cables would probably be preferred for connections of medium length (e.g. 300 m), while preference would go to optical fibres for very long connection lengths. It is possible to implement a system for detection of the occurrence of errors at the receiving end of the connection and thus automatically monitoring its performance. In a fully integrated digital installation or system it may be useful for all interconnections to be transparent to any appropriate digital stream, irrespective of the message content. Thus, although the interface will be used to transmit a video signal, it should be “transparent” to the message content, i.e. it should not base its operation on the known structure of the message itself. The multiplexed data stream of 10-bit words (as described in Part 1) is transmitted over a single channel in bit-serial form. Prior to transmission, additional coding takes place to provide spectral shaping, word synchronization and to facilitate clock recovery. 2 Coding The uncoded serial bit-stream is scrambled using the generator polynomial G1(x) × G2(x), where: G1(x)  x9 + x4 + 1 to produce a scrambled NRZ signal, and G2(x)  x + 1 to produce a polarity-free NRZI sequence. 3 Order of transmission The least significant bit of each 10-bit word shall be transmitted first. 4 Logic convention The signal is transmitted in NRZI form, for which the bit polarity is irrelevant. 5 Transmission medium The bit-serial data stream can be conveyed using either a coaxial cable (see § 6) or fibre-optic bearer (see § 7). 6 Characteristics of the electrical interface 6.1 Line driver characteristics (source) 6.1.1 Output impedance The line driver has an unbalanced output with a source impedance of 75  and a return loss of at least 15 dB over a frequency range of 5-270 MHz. 6.1.2 Signal amplitude The peak-to-peak signal amplitude lies between 800 mV  10 measured across a 75  resistive load directly connected to the output terminals without any transmission line. 6.1.3 DC offset The DC offset with reference to the mid-amplitude point of the signal lies between +0.5 and –0.5 V. 6.1.4 Rise and fall times The rise and fall times, determined between the 20 and 80 amplitude points and measured across a 75  resistive load connected directly to the output terminals, shall lie between 0.75 and 1.50 ns and shall not differ by more than 0.50 ns. 6.1.5 Jitter The output jitter is specified as follows: Output jitter (see Note 1) f1  10 Hz f3  1 kHz f4  1/10 of the clock rate A1  0.2 UI (UI; unit interval) A2  0.2 UI NOTE 1 – 1 UI corresponds to. 3.7 ns 0.2 UI correspond to 0.74 ns. Specification of jitter and jitter measurements methods shall comply with Recommendation ITU‑R BT.1363 (Jitter specifications and jitter measurement methods of bit-serial signals conforming to Recommendations ITU-R BT.656, ITU-R BT.799 and ITU-R BT.1120). 6.2 Line receiver characteristics (destination) 6.2.1 Terminating impedance The cable is terminated by 75  with a return loss of at least 15 dB over a frequency range of 5‑270 MHz. 6.2.2 Receiver sensitivity The line receiver must sense correctly random binary data when either connected to a line driver operating at the extreme voltage limits permitted by § 6.1.2 or when connected via a cable having a loss of 40 dB at 270 MHz and a loss characteristic of 1 / . 6.2.3 Interference rejection When connected directly to a line driver operating at the lower limit specified in § 6.1.2, the line receiver must sense correctly the binary data in the presence of a superimposed interfering signal at the following levels: DC  2.5 V Below 1 kHz: 2.5 V peak-to-peak 1 kHz to 5 MHz: 100 mV peak-to-peak Above 5 MHz: 40 mV peak-to-peak 6.3 Coaxial cables and connectors 6.3.1 Cable It is recommended that the coaxial cable chosen should meet any relevant national standards on electromagnetic radiation. NOTE 1 – Processing and transmission of digital data, such as digital video signals at high data rates produces a wide spectrum of energy that has the potential to cause cross-talk or interference. It should be noted that the ninth and eighteenth harmonics of the 13.5 MHz sampling frequency (nominal value) specified in Recommendation ITU-R BT.601 fall at the 121.5 and 243 MHz aeronautical emergency channels. Appropriate precautions must therefore be taken in the design and operation of interfaces to ensure that no interference is caused at these frequencies. Permitted maximum levels of radiated signals from digital data processing equipment are the subject of various national and international standards, and it should be noted that emission levels for related equipment are given in CISPR Recommendation: “Information technology equipment – limits of interference and measuring methods” (Doc. CISPR/B (Central Office) 16). Nevertheless, RR No. 4.22 prohibits any harmful interference on the emergency frequencies (see also Recommendation ITU‑R BT.803). NOTE 2 – Transmission by optical fibres eliminates radiation generated by the cable and also prevents conducted common-mode radiation, but the performance of coaxial cable can also be made near perfect. It is believed that the major portion of any radiation would be from the processing logic and high-power drivers common to both methods. Due to the wideband, random nature of the digital signal, little is gained by frequency optimization. 6.3.2 Characteristic impedance The coaxial cable used shall have a nominal characteristic impedance of 75 . 6.3.3 Connector characteristics The connector shall have mechanical characteristics conforming to the standard BNC type (IEC 61169-8 (2007-2))* – Part 8: Sectional specification – RF coaxial connectors with inner diameter of outer conductor 6.5 mm (0.256 in) with bayonet lock-characteristic impedance 50 Ω (type BNC), Annex A (Normative) Information for interface dimensions of 75 Ω characteristic impedance connector with unspecified reflection factor.. 7 Characteristics of the optical interface Specifications for the characteristics of the optical interface should comply with general rules of Recommendation ITU‑R BT.1367 (Serial Digital Fiber Transmission Systems for Signals Conforming to Recommendations ITU-R BT.656, ITU-R BT.799 and ITU-R BT.1120). To make use of this Recommendation the following specifications are necessary: Rise and fall times  1.5 ns (20 to 80) Output jitter (see Note 1) f1  10 Hz f3  1 kHz f4  1/10 of the clock rate A1  0.135 UI (UI; unit interval) A2  0.135 UI NOTE 1 – Specification of jitter and jitter measurements methods shall comply with Recommendation ITU‑R BT.1363 (Jitter specifications and jitter measurement methods of bit-serial signals conforming to Recommendations ITU-R BT.656, ITU-R BT.799 and ITU-R BT.1120). Appendix 1 (Informative) Bit-parallel interface1 1 General description of the interface The bits of the digital code words that describe the video signal are transmitted in parallel by means of eight (optionally, ten) conductor pairs, where each carries a multiplexed stream of bits (of the same significance) of each of the component signals, CB, Y, CR, Y. The eight pairs also carry ancillary data that is time-multiplexed into the data stream during video blanking intervals. An additional pair provides a synchronous clock at 27 MHz. The signals on the interface are transmitted using balanced conductor pairs. Cable lengths of up to 50 m ( 160 feet) without equalization and up to 200 m ( 650 feet) with appropriate equalization may be employed. The interconnection employs a twenty-five pin D-subminiature connector equipped with a locking mechanism (see § 5). For convenience, the bits of the data word are assigned the names DATA 0 to DATA 9. The entire word is designated as DATA (0-9). DATA 9 is the most significant bit. Eight-bit data words occupy DATA (2-9). Video data is transmitted in NRZ form in real-time (unbuffered) in blocks, each comprising one active television line. 2 Data signal format The interface carries data in the form of eight or ten parallel data bits and a separate synchronous clock. Data is coded in NRZ form. The recommended data format is described in Part 1. 3 Clock signal 3.1 General The clock signal is a 27 MHz square wave where the 0-1 transition represents the data transfer time. This signal has the following characteristics: Width: 18.5  3 ns Jitter: Less than 3 ns from the average period over one field. NOTE 1 – This jitter specification, while appropriate for an effective parallel interface, is not suitable for clocking digital-to-analogue conversion or parallel-to-serial conversion. 3.2 Clock-to-data timing relationship The positive transition of the clock signal shall occur midway between data transitions as shown in Fig. 2. 4 Electrical characteristics of the interface 4.1 General Each line driver (source) has a balanced output and the corresponding line receiver (destination) a balanced input (see Fig. 3). Although the use of ECL technology is not specified, the line driver and receiver must be ECL‑compatible, i.e. they must permit the use of ECL for either drivers or receivers. All digital signal time intervals are measured between the half-amplitude points. 4.2 Logic convention The A terminal of the line driver is positive with respect to the B terminal for a binary 1 and negative for a binary 0 (see Fig. 3). 4.3 Line driver characteristics (source) 4.3.1 Output impedance: 110  maximum. 4.3.2 Common mode voltage: –1.29 V  15 (both terminals relative to ground). 4.3.3 Signal amplitude: 0.8 to 2.0 V peak-to-peak, measured across a 110  resistive load. 4.3.4 Rise and fall times: less than 5 ns, measured between the 20 and 80 amplitude points, with a 110  resistive load. The difference between rise and fall times must not exceed 2 ns. 4.4 Line receiver characteristics (destination) 4.4.1 Input impedance: 110   10 . 4.4.2 Maximum input signal: 2.0 V peak-to-peak. 4.4.3 Minimum input signal: 185 mV peak-to-peak. However, the line receiver must sense correctly the binary data when a random data signal produces the conditions represented by the eye diagram in Fig. 4 at the data detection point. 4.4.4 Maximum common mode signal:  0.5 V, comprising interference in the range 0 to 15 kHz (both terminals to ground). 4.4.5 Differential delay: Data must be correctly sensed when the clock-to-data differential delay is in the range between  11 ns (see Fig. 4). 5 Mechanical details of the connector The interface uses the 25 contact type D subminiature connector specified in ISO Document 2110-1980, with the contact assignment shown in Table 4. Connectors are locked together by two UNC 4-40 screws on the cable connectors, which go in female screw locks mounted on the equipment connector. Cable connectors employ pin contacts and equipment connectors employ socket contacts. Shielding of the interconnecting cable and its connectors must be employed (see Note 1). TABLE 4 Contact assignments

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