| 摘要 |
<p>A horizontal line counter (110, 115, 120) provides a signal (LINE Nr. 21) identifying the beginning of video data in a particular horizontal vido line. The counter is clocked by multiple clock signals. A first clock signal (HOR PLS) clocks the counter until the line count value equals a known value that is less than the line number of the horizontal line that is to be identified. When the count value equals the known value, clocking by a second clock signal (COMP SYNC) is enabled. Although, the first clock source provides a regular pulse waveform suitable for clocking the counter reliably, transitions on the first clock signal may not accurately indicate the beginning of information within a horizontal line interval. Transitions on the second clock signal accurately indicate the beginning of the desired information. However, the wave form of the second clock signal may exhibit irregularities prior to the time at which clocking by the second clock signal is enabled that could adversely affect the reliability of the counter value. The combined clocking arrangement advantageously provides significantly higher reliability of the count value and improves the timing of the line identification signal with respect to the beginning of the desired video data.</p> |
