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2. Reference Information
2-1 The Closed Caption Signal
The caption signal associated with a television program is transmitted as an encoded composite data
signal during line 21 of field one of the standard NTSC video signal as shown in Fig. 2-1. The signal
consists of a Clock Run-in signal, a start bit and 16 bits of data. Transmission of actual data amounts to
16 bits every 1/30 of a second or 480 bits per second. The phases of the clock run-in signal (503KHz, 7
cycles) and the data code are synchronized. After the clock run-in signal is held at logic level Ò0Ó for 2
bits then the start bit (logic 1) followed by 16 data bits are transmitted. The data may be either charac-
ters for display, attribute codes or control codes.
1'st Field
1
525
2'nd Field
264
Samsung Electronics
V Flyback Period
2
3
4
5
6
265
266
267
268
Fig. 2-1 Video Signal
CLOCK
RUN IN
Line 21
Fig. 2-2 Caption Data
7
8
9
10
269
270
271
272
273
16BIT NRZ DATA
START BIT
11
19
20
Line 21
274
282
283
COLOR BURST
0 IRE
Reference Information
Line 284
2-1
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