ADV7170/ADV7171
APPENDIX 3—COPY GENERATION MANAGEMENT SYSTEM (CGMS)
The ADV7170/ADV7171 support copy generation management systems (CGMS) conforming to the standard. CGMS data is transmitted
on Line 20 of the odd fields and Line 283 of even fields. Bit C/W05 and Bit C/W06 control whether or not CGMS data is output on odd
and even fields. CGMS data can only be transmitted when the ADV7170/ADV7171 are configured in NTSC mode.
The CGMS data is 20 bits long; the function of each of these bits is 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 the Bit C/W04 is set to a Logic Level 1, the last six bits, C19 to C14, which comprise the 6-bit CRC check sequence, are calculated
automatically on the ADV7170/ADV7171 based on the lower 14 bits (C0 to 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 Level 0, all 20 bits (C0 to 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
Word 1
Word 2
CRC
–
–
–
–
6 Bits
4 Bits
6 Bits
6 Bits
CRC Polynomial = X6 + X + 1 (Preset to 111111)
0
Word 0
B1
1
Aspect Ratio
Display Format
Undefined
16:94:3
B2
Letterbox
Normal
B3
Word 0
B4, B5, B6
Word 1
Identification information about video and other signals (for example, audio)
Identification signal incidental to Word 0
B7, B8, B9, B10
Word 2
B11, B12, B13, B14
Identification signal and information incidental to Word 0
+100 IRE
+70 IRE
CRC SEQUENCE
REF
C0 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19
0 IRE
49.1μs ± 0.5μs
–40 IRE
11.2μs
2.235μs ± 20ns
Figure 57. CGMS Waveform Diagram
Rev. C | Page 41 of 64
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