z86229 ZiLOG Semiconductor, z86229 Datasheet - Page 18

• Manufacturer Part Number: z86229
• Description: Z86229 Ntsc Line 21 Ccd Decoder
• Manufacturer: ZiLOG Semiconductor

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21 waveform in the video field corresponding to the
data channel selected for display. The decoder is held
in the Decoder OFF (TV) state until a Line 21
waveform is continuously detected for a period of 0.5
seconds. After a valid Line 21 waveform has been
detected for 0.5 seconds, and assuming that the user
has selected the Decoder ON state, the normal display
for the data channel selected is presented. The
autoblanking circuit is not activated again until a valid
Line 21 waveform has been lost for 1.5 seconds. Any
data received during the 1.5-second period resets the
counter. As a result, autoblanking is only activated on
continuous loss of the Line 21 waveform for 1.5
seconds.
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Note:
4. The fourth method of clearing the screen is by the
action of the 16-Second Erase Timer. This function is
only active when a CAPTION or XDS display mode
has been selected. If no data is received for the display
channel selected for a 16-Second period, the on-screen
memory is erased; however, the decoder is still on the
selected channel (with the decoder ON), allowing data
for the selected channel to be displayed.
A valid Line 21 waveform is defined as the presence of a
7-cycle run-in clock, in addition to a start bit on Line 21
of the field being examined.
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