1、Rec. ITU-R BT.1304 1RECOMMENDATION ITU-R BT.1304CHECKSUM FOR ERROR DETECTION AND STATUSINFORMATION IN INTERFACES CONFORMING WITHRECOMMENDATIONS ITU-R BT.656 AND ITU-R BT.799(Question ITU-R 65/11)(1997)Rec. ITU-R BT.1304The ITU Radiocommunication Assembly,consideringa) that many countries are install
2、ing digital television production facilities based on the use of digital videocomponents conforming to Recommendations ITU-R BT.601 and ITU-R BT.656;b) that there exists the capacity within a signal conforming to Recommendation ITU-R BT.656 for additional datasignals to be multiplexed with the video
3、 data signal itself;c) that there are operational and economic benefits to be achieved by the multiplexing of ancillary data signalswith the video data signal;d) that the operational benefits are increased if a minimum of different formats are used for ancillary data signals;e) that some countries a
4、re already using ancillary data signals embedded in the video data signal,recommends1 that for optional error detection and provision of status information the methods described in Annex 1 for thegeneration of checkwords and status flags should be used in interfaces conforming with Recommen-dations
5、ITU-R BT.656 and ITU-R BT.799.ANNEX 1Checksum for error detection and status information1 IntroductionThis specification describes the generation of error detection checkwords and related status flags to be used optionally inconjunction with the serial digital interface described in Recommendation I
6、TU-R BT.656.Two checkwords are defined: one based on a field of active picture video data words and the other on a full field of datawords. This two-word approach provides continuing error detection for the active picture when the digital signal haspassed through processing equipment that has change
7、d the data outside the active picture area without recalculating thefull-field checkword.Three sets of flags are provided to feed forward information regarding detected errors to help facilitate identification offaulty equipment and the type of fault. One set of flags is associated with each of the
8、two field related checkwords. Athird set of flags is used to provide similar information based on evaluating all of the ancillary data checksums within afield. Implementation of these flags is optional.2 Rec. ITU-R BT.1304The checkwords and flags are combined in an error detection data packet which
9、is included as ancillary data. At thereceiver, a recalculation of checkwords may be compared to the error detection data packet information to determine if atransmission error has occurred.2 Location of checkwords, flags, identification number, and included samples2.1 Location of checkwords, flags a
10、nd identification numberData packets containing the calculated checkwords, error information flags and identification number are located in theancillary data area of the vertical interval as shown graphically in Figs. 1a and 1b and specified in Table 1 for 525/59.94systems and Table 2 for 625/50 sys
11、tems. These locations are chosen to respect the location of source switching points.The error detection data packet is located immediately prior to the start of active video (SAV) code words in the lineprior to that during which source switching occurs.TABLE 1Location of 525/59.94 system checkwordsE
12、rror checking data locations: line 9, fields I and III andline 272, fields II and IVData item Word No.Ancillary Data Flag word 1 1 689 (00.0h)Ancillary Data Flag word 2 1 690 (FF.Ch)Ancillary Data Flag word 3 1 691 (FF.Ch)Data Identifier 1 692 (7D.0h)Data Block Number 1 693 (80.0h)Data Count 1 694 (
13、44.0h)Active picture data word 0 1 695Active picture data word 1 1 696Active picture data word 2 1 697Full-field data word 0 1 698Full-field data word 1 1 699Full-field data word 2 1 700Ancillary data error flags 1 701Active picture error flags 1 702Full-field error flags 1 703Reserved words (7 tota
14、l) 1 704-1 710Checksum for this ancillary data packet 1 711NOTE 1 Values in parentheses are sample values.Rec. ITU-R BT.1304 31304-01a1689-17111440 1444 1711 1715 0 143989101112132021262263271272273274275283284525EAV SAVeefeeaeefaaaaaafffccceeafffcccFIGURE 1aLocation of checkwords and included sampl
15、es (525-line systems)EAV: end of active video.Note 1 See Table 1 for exact sample locations in both fields.Note 2 ccc: location of checkwords and status flags.Note 3 fff: first sample included in the full-field checkword.Note 4 aaa: first sample included in the active picture checkword.Note 5 eea: l
16、ast sample included in the active picture checkword.Note 6 eef: last sample included in the full-field checkword.Line No. 1Switching line(This line is not included in full-field sample)(This line is first full-field sample)(This line is first active picture sample)Active videoSwitching line(This lin
17、e is not included in full-field sample)(This line is first full-field sample)(This line is first active picture sample)Active videoFIGURE 1304-01a = page pleine4 Rec. ITU-R BT.13041304-01b1440 1444 1723 1727 0 143914106255678911222324310311317318319320321335336622EAV SAVeefeefaaaaaafffccceeafffcccee
18、aFIGURE 1bLocation of checkwords and included samples (625-line systems)Note 1 See Table 2 for exact sample locations in both fields.Note 2 ccc: location of checkwords and status flags.Note 3 fff: first sample included in the full-field checkword.Note 4 aaa: first sample included in the active pictu
19、re checkword.Note 5 eea: last sample included in the active picture checkword.Note 6 eef: last sample included in the full-field checkword.Line No. 624Switching line(This line is not included in full-field sample)(This line is first full-field sample)(This line is first active picture sample)Active
20、videoSwitching line(This line is not included in full-field sample)(This line is first full-field sample)(This line is first active picture sample)Active videoFIGURE 1304-01b = page pleineRec. ITU-R BT.1304 5TABLE 2Location of 625/50 system checkwords2.2 Samples included in checkword calculationsSta
21、rting and ending samples for active picture and full-field checkword calculations are shown in Table 3. For the activepicture checkword, only the samples in the digital active picture area of each line are included in the calculation.Full-field checkwords include all the samples in all lines except
22、the line containing the error detection data packet andthe two following lines.TABLE 3Checkword included samplesError checking data locations: line 5, field I andline 318, fields IIData item Word No.Ancillary Data Flag word 1 Y 850 (00.0h)Ancillary Data Flag word 2 Cr425 (FF.Ch)Ancillary Data Flag w
23、ord 3 Y 851 (FF.Ch)Data Identifier Cb426 (7D.0h)Data Block Number Y 852 (80.0h)Data Count Cr427 (44.0h)Active picture data word 0 Y 853Active picture data word 1 Cb428Active picture data word 2 Y 854Full-field data word 0 Cr429Full-field data word 1 Y 855Full-field data word 2 Cb430Ancillary data er
24、ror flags Y 856Active picture error flags Cr431Full-field error flags Y 857Reserved words (7 total) Cb432Checksum for this ancillary data packet Y 858NOTE 1 Values in parentheses are sample values.Data item 13.5 MHz component525/59.94 systemsFirst full-field sample, lines 12 and 275 1 444First activ
25、e picture sample, lines 21 and 284 0Last active picture sample, lines 262 and 525 1 439Last full-field sample, lines 8 and 271 1 439625/50 systemsFirst full-field sample, lines 8 and 321 Cb361First active picture sample, lines 24 and 336 Cb0Last active picture sample, lines 310 and 622 Y 719Last ful
26、l-field sample, lines 4 and 317 Y 7196 Rec. ITU-R BT.13043 Definitions of data words3.1 Checkword valuesEach checkword value consists of 16 bits of data calculated using the Cyclic Redundancy Check (CRC) polynomialgeneration method. The equation and a conceptual logic diagram (see Fig. 2) are shown
27、below:Checkword (16 bit) = x16+ x12+ x5+ 11304-02151413121 10987654 3210FIGURE 2Serial dataFIGURE 1304-02 = 3 cmAll data words with values between FF.0hand FF.8hinclusive are recoded to FF.Chat the input to the CRC polynomialgenerator. This recoding is necessary only at the polynomial generator, for
28、 the purposes of ensuring compatibilitybetween 8-bit and 10-bit equipment and between different implementations of serial digital interface time referencesignals and ancillary data flag coding.3.2 Ancillary data housekeeping, checkwords and flagsDefinitions of each ancillary data word specified are
29、shown in Table 4. Zeros are used in the two least significant bits(LSBs) of all words in the data packet to provide compatibility with 8-bit equipment. Bit b7(V) in picture/field dataword 3 is a 1 if a valid CRC has been calculated. A P in b8provides even parity for b7through b0; that is, the totaln
30、umber of 1s in b8-b0is an even number. The most significant bit (MSB), b9, is the logical inverse of b8. A checksum isthe last word in the error detection data packet.The checksum word is used to determine the validity of the included words. The checksum word consists of 9 bits and isthe sum of the
31、9 LSBs (b8-b0) of all words including the Data Identifier (DID) and the Reserved Words. The sum ispreset to all zeros at the start of each calculation and the carry ignored.3.3 Error flags3.3.1 Definition of individual error status flagsAll error flags indicate only the status of the previous field;
32、 that is, each flag is set or cleared on a field-by-field basis. Alogical 1 is the set state and a logical 0 is the unset state. The flags are defined as follows:edh error detected here: signifies that a serial transmission error was detected. In the case of ancillary data,this means that one or mor
33、e ancillary data blocks did not match its checksum.eda error detected already: signifies that a serial transmission error has been detected at a prior point in thesignal path. If a device receives a signal in which the edh flag has been set, thenthat device will forward the data with the eda flag se
34、t and the edh flag set to zero ifthere is no further error in the data.Rec. ITU-R BT.1304 7idh internal error detected here: signifies that a hardware error unrelated to serial transmission has been detectedwithin a device. This is provided specifically for devices which have internal error-checking
35、 facilities, as an error reporting mechanism.ida internal error detected already: signifies that an idh flag was received and there was a hardware device failure at aprior point in the signal chain.ues unknown error status: signifies that a serial signal was received from a device not supporting thi
36、s error-detection practice.TABLE 4Definition of ancillary data words3.3.2 Degrees of implementationIndividual error status flags, or all such flags, may not be supported by all equipment. To maintain compatibility withfull implementations of this specification, in all such cases where one or more er
37、ror status flags are not supported, theunsupported flags are set to zero.Data itemb9MSBb8b7b6b5b4b3b2b1b0LSBAncillary data header, ancillary data flag (ADF), word 1 0 0 0 0 0 0 0 0 0 0Ancillary data header, ADF, word 2 1 1 1 1 1 1 1 1 1 1Ancillary data header, ADF, word 3 1 1 1 1 1 1 1 1 1 1Data ide
38、ntifier (7D.0h) 0 11111 0 1 0 0Data block number (80.0h) 1 00000 0 0 0 0Data count (44.0h) 0 10001 0 0 0 0Active picture data count word 0 CRC P/ P c c c c c c 0 0Active picture data count word 1 CRC P/ P c c c c c c 0 0Active picture data count word 0 CRC P/ P V 0 c c c c 0 0Full-field data word 0
39、CRC P/ P c c c c c c 0 0Full-field data word 0 CRC P/ P c c c c c c 0 0Full-field data word 0 CRC P/ P V 0 c c c c 0 0Ancillary data error flags P/ P 0 ues ida idh eda edh 0 0Active picture error flags P/ P 0 ues ida idh eda edh 0 0Full-field error flags P/ P 0 ues ida idh eda edh 0 0Reserved words (7 total) 1/ 0 0 0 0 0 0 0 0 0Checksum S8/ S8 S7 S6 S5 S4 S3 S2 S1 S0NOTE 1 P and V are defined in 3.2.
