CEA-516-1988.pdf
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1、 CEA Standard Joint EIA/CVCC Recommended Practice for Teletext: North American Basic Teletext Specification (NABTS) CEA-516 May 1988 Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 20:33
2、:30 MDTNo reproduction or networking permitted without license from IHS -,-,- NOTICE CEA Standards, Bulletins and other technical publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and imp
3、rovement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need. Existence of such Standards, Bulletins and other technical publications shall not in any respect preclude any member or nonmember of CEA from manufacturing or s
4、elling products not conforming to such Standards, Bulletins or other technical publications, nor shall the existence of such Standards, Bulletins and other technical publications preclude their voluntary use by those other than CEA members, whether the standard is to be used either domestically or i
5、nternationally. Standards, Bulletins and other technical publications are adopted by CEA in accordance with the American National Standards Institute (ANSI) patent policy. By such action, CEA does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties ado
6、pting the Standard, Bulletin or other technical publication. This CEA Standard is considered to have International Standardization implication, but the International Electrotechnical Commission activity has not progressed to the point where a valid comparison between the CEA Standard and the IEC doc
7、ument can be made. This Standard does not purport to address all safety problems associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this Standard to establish appropriate safety and health practices and to determine the applicability of regulat
8、ory limitations before its use. (From Project Number 1836, formulated under the cognizance of the CEA R4.3 Television Data Systems Subcommittee.) Published by CONSUMER ELECTRONICS ASSOCIATION 2002 Technology the Packet Prefix, the Data Block and the optional Suffix. The structure of the Data Packet
9、is illustrated in Figure 6. 3.2 PACKET PREFIX 3.2.1 Structure of the Packet Prefix The Packet Prefix shall immediately follow the Synchronization Sequence specified in 2.2. The Packet Pref1x consists of five bytes in the following order: Pl,P2,P3,CI,PS where Pl,P2,P3 = Packet Address bytes CI = Cont
10、inuity Index Byte PS = Packet Structure Byte 3.2.2 Coding of the Packet Prefix Bytes All the bytes of the Packet Prefix are Hamming encoded. In these bytes, bits 7, 5, 3 and 1 provide protection for the informat1on bits 8, 6, 4. and 2, and also maintain odd parity over the Hamming byte. The Hamming
11、encoding and decoding for each byte are shown in Figure 7. This method of data protection allows the correction of all single-bit errors, and the detection of all two-bit errors in each byte. 3.2.3 Packet Address (P) The first three bytes of the Packet Prefix, PI, P2 and P3, define the Packet Addres
12、s, P, with PI being the most significant byte. Each byte contains four information bits, which define a hexadecimal digit (0 through F) .There are 4096 possible Packet Addresses. The Packet Address is identical to the Data Channel number. These Packet Addresses may be used by more than one service a
13、nd are not sufficient as a means of identifying teletext data, see 4.2.2. 3.2.4 Continuity Index (CI) The Continuity Index is the fourth Hamming-encoded byte of the Packet Prefix. The value or number of the continuity Index sequences from 0 to 15. It increments by one each time a Data Packet is tran
14、smitted within a given Data channel unless the Data Packet is a Synchronizing Packet as def1ned in 3.2.5. If the Data Packet is a synchronizing Packet, then the Continuity Index may not be related to the continuity Index of the preceding Data Packet in the Data Channel. Copyright Consumer Electronic
15、s Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 20:33:30 MDTNo reproduction or networking permitted without license from IHS -,-,- Page 6 CEA 516 The Continuity Index is used to detect the loss of a Data Packet in a
16、 Data Group due to transmission or other errors. 3.2.5 Packet Structure Byte (PS The Packet Structure Byte is the fifth and last byte of the Packet Prefix. This byte specifies the type of Data Packet, whether the Data Packet is full, and the length of the Suffix. Bit b2 specifies the type of Data Pa
17、cket. Specifically, b2=1 indicates that the packet is a Synchronizing Packet, which starts a Data Group, see 4.1; and b2=O indicates that e packet is a Standard Packet, which is part of a Data Group. Bit b4 specifies whether the Data Packet is full. Specifically, b4=O indicates that the Data Packet
18、is full of useful data, and b4=1 indicates that the Data Packet is not completely full of useful data. The last Data Packet in a Data Group is not necessarily indicated by b4 = 1. Bits b6 and b8 specify the length of the suffix, which is described in 3.4. 3.3 DATA BLOCK The Data Block consists of th
19、e group of bytes that follow the Packet Prefix and precede the Suffix, if any. The Data Block may be full or not full of useful data in accordance with bit b4 of the Packet Structure Byte specified in 3.2.5. The length of the Data Block depends on the length of the Suffix, and can have values of zer
20、o, 26, 27 or 28 bytes. All bytes within Data Blocks belonging to Data Group Type zero, see 4.2.2, shall be transmitted with odd parity. Some bytes are Hamming-encoded, as described in 3.2.2, and the Hamming code was chosen to provide odd parity. The other bytes shall be transmitted with the most sig
21、nificant bit, b8, in each byte used for odd parity. 3.4 SUFFIX The Suffix consists of one or more bytes, which may be used by the receiver to either detect or detect and correct transmission errors in the Data Block. The Suffix, if present, shall be placed at the end of the Data Packet following the
22、 Data Block. Even if the Data Block is not full of useful information, the Suffix, if present, shall be positioned at the end of the Data Packet as shown in Figure 6. The length of the Suffix is indicated by bits b8 and b6 of the Packet Structure Byte (see 3.2.5). Note that the maximum length of the
23、 Data Block is reduced by the number of Suffix bytes. The error-protection schemes specified by bits b8 and b6 of PS shall be: Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 20:33:30 MD
24、TNo reproduction or networking permitted without license from IHS -,-,- CEA 516 Page 7 b8 b6 length format 0 0 0 no Suffix 0 1 1 byte longitudinal parity- check byte 1 0 2 byte last byte shall be longitudinal parity check , second to last byte is subject to further study. An error- protection byte b
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