CH7004C Datasheet, PDF (40/51 Pages) List of Unclassifed Manufacturers – Digital PC to TV Encoder with Macrovision

CHRONTEL
CH7004C
Register Descriptions (continued)
2. Set the SENSE bit to a 1. This forces a constant current output onto the Y, C, and CVBS outputs. Note that
during SENSE = 1, these 3 analog outputs are at steady state and no TV synchronization pulses are asserted.
3. Reset the SENSE bit to 0. This triggers a comparison between the voltage sensed on these analog outputs
and the reference value expected (V_threshold = 1.235V). If the measured voltage is below this threshold
value, it is considered connected, if it is above this voltage it is considered unconnected. During this step,
each of the three status bits corresponding to individual analog outputs will be set if they are NOT
connected.
4. Read the status bits. The status bits, Y, C, and CVBST (corresponding to S-Video Y and C outputs and
composite video) now contain valid information which can be read to determine which outputs are
connected to a TV. Again, a “0” indicates a valid connection, a “1” indicates an unconnected output.
Contrast Enhancement Register
Symbol: CE
Address: 11H
Bits: 3
Bit:
7
6
5
4
3
2
1
0
Symbol:
CE2
CE1
CE0
Type:
R/W
R/W
R/W
Default:
0
1
1
This register provides control of the contrast enhancement feature of the CH7004, according to the table below. At a
setting of 000, the video signal will be pulled towards the maximum black level. As the value of CE[2:0] is
increased, the amount that the signal is pulled towards black is decreased until unity gain is reached at a setting of
011. From this point on, the video signal is pulled towards the white direction, with the effect increasing with
increasing settings of CE[2:0].
Table 24. Contrast Enhancement Function
CE[2:0]
000
001
010
011
100
101
110
111
Description (all gains limited to 0-255)
Contrast enhancement gain 3 Y_out = (5/4)*(Y_in-102) = Enhances Black
Contrast enhancement gain 2 Y_out = (9/8)*(Y_in-57)
Contrast enhancement gain 1 Y_out = (17/16)*(Y_in-30)
Normal mode Y_out = (1/1)*(Yin-0) = Normal Contrast
Contrast enhancement gain 1 Y_out = (17/16)*(Y_in-0)
Contrast enhancement gain 2 Y_out = (9/8)*(Y_in-0)
Contrast enhancement gain 3 Y_out = (5/4)*(Y_in-0)
Contrast enhancement gain 4 Y_out = (3/2)*(Y_in-0) = Enhances White
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201-0000-024 Rev 2.1, 8/2/99