ADV7174BCP datasheet(42/52 Pages) AD

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ADV7174/ADV7179

Rev. A | Page 42 of 52

APPENDIX 3—COPY GENERATION MANAGEMENT SYSTEM (CGMS)

The ADV7174/ADV7179 supports the CGMS, conforming to

the standard. CGMS data is transmitted on Line 20 of the odd

fields and on Line 283 of the even fields. Bits C/W05 and

C/W06 control whether or not CGMS data is output on odd

and even fields. CGMS data can only be transmitted when the

ADV7174/ ADV7179 is configured in NTSC mode. The CGMS

data is 20 bits long, the function of each of these bits is as shown

below. The CGMS data is preceded by a reference pulse of the

same amplitude and duration as a CGMS bit (see Figure 57).

The bits are output from the configuration registers in the

following order: C/W00 = C16, C/W01 = C17, C/W02 = C18,

C/W03 = C19, C/W10 = C8, C/ W11 = C9, C/W12 = C10,

C/W13 = C11, C/W14 = C12, C/ W15 = C13, C/W16 = C14,

C/W17 = C15, C/W20 = C0, C/W21 = C1, C/W22 = C2, C/W23

= C3, C/W24 = C4, C/W25 = C5, C/W26 = C6, C/W27 = C7. If

Bit C/W04 is set to a Logic 1, the last six bits, C19–C14, which

comprise the 6-bit CRC check sequence, are calculated

automatically on the ADV7174/ADV7179 based on the lower

14 bits (C0–C13) of the data in the data registers and output

with the remaining 14 bits to form the complete 20 bits of the

CGMS data. The calculation of the CRC sequence is based on

the polynomial X6 + X + 1 with a preset value of 111111. If

C/W04 is set to a Logic 0, all 20 bits (C0–C19) are directly

output from the CGMS registers (no CRC is calculated; it must

be calculated by the user).

FUNCTION OF CGMS BITS

Word 0 –6 Bits

Word 1 –4 Bits

Word 2 –4 Bits

CRC –6 Bits CRC Polynomial = X6 + X + 1 (Preset to 111111)

Table 21. Bit 1–Bit 14

Word

Bit

Function

Word 0

Aspect Ratio

16:9

4:3

Display Format

Letterbox

Normal

Undefined

B4, B5, B6

Identification information about video and other signals, for example, audio

Word 1

B7, B8, B9, B10

Identification signal incidental to Word 0

Word 2

B11, B12, B13, B14

Identification signal and information incidental to Word 0

CRC SEQUENCE

11.2

µs

2.235

µs ± 20ns

49.1

µs ± 0.5µs

REF

C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19

100 IRE

70 IRE

0 IRE

–40 IRE

Figure 57. CGMS Waveform Diagram

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