msm7654 Oki Semiconductor, msm7654 Datasheet - Page 23

• Manufacturer Part Number: msm7654
• Description: Ntsc/pal Digital Video Encoder
• Manufacturer: Oki Semiconductor

The normal vertical blanking periods cannot be obtained in the following cases:
(1) If the HSYNC_L peiod is longer than the standard, the vertical blanking period is output in
(2) If the HSYNC_L period is shorter than the standard, serrations may be lost.
(3) If the VSYNC_L period is longer than the standard, the vertical blanking period is output as
• If the number of lines is greater than the standard value, the first equalizing pulse period is
• If the number of lines is equal to the standard value, the contents of output signals per line
• If the number of lines is smaller than the standard value, the first equalizing pulse period is
(4) If the VSYNC_L period is shorter than the standard, the vertical blanking period is output as
• If the number of lines is greater than the standard value, the first equalizing pulse period is
• If the number of lines is equal to the standard value, the contents of output signals per line
• If the number of lines is smaller than the standard value, the first equalizing pulse period is
¡ Semiconductor
the HSYNC_L period unless the pixel counter overflows in one line.
However, in the waveform the front porch period becomes longer.
When the pixel counter overflows, the encoder recognizes that the HSYNC_L signal has been
input when the pixel counter becomes zero and the next line starts.
The following HSYNC_L signal resets the pixel counter again.
Therefore, inputting such a signal not only disturbs signals in the vertical blanking period but
also causes abnormal operations in the horizontal period.
shown below.
longer.
are normal.
shorter.
shown below.
longer.
are normal.
shorter.
HSYNC_L (normal)
VSYNC_L
HSYNC_L (Long)
Composite (Output)
The front porch period is longer
than when the normal HSYNC_L
signal is input.
Front Porch
MSM7654
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