ch7008a Chrontel, ch7008a Datasheet - Page 31

• Manufacturer Part Number: ch7008a
• Description: Digital Pc To Tv Encoder
• Manufacturer: Chrontel

CHRONTEL
Register Descriptions (continued)
2. Ensure that the XCLK and XCLK* input pins are receiving clock signals (alternatively, XCLK* can be
3. Set the SENSE bit to a 1. This forces a constant current output onto the Y, C, and CVBS outputs. Note that
4. Reset the SENSE bit to 0. This triggers a comparison between the voltage sensed on these analog outputs
5. Read the status bits. The status bits Y, C and CVBST (corresponding to S-Video Y and C outputs and
Contrast Enhancement Register
This register provides control of the contrast enhancement feature of the CH7008, 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].
201-0000-027 Rev 2.8, 6/24/2004
Table 20. Contrast Enhancement Function
Bit:
Symbol:
Type:
Default:
CE[2:0]
000
001
010
011
100
101
110
111
connected to the VREF pin).
during SENSE = 1, these 3 analog outputs are at steady state and no TV synchronization pulses are asserted.
and the reference value expected (V
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.
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.
7
Contrast enhancement gain 3 Y
Contrast enhancement gain 2 Y
Contrast enhancement gain 1 Y
Normal mode Y
Contrast enhancement gain 1 Y
Contrast enhancement gain 2 Y
Contrast enhancement gain 3 Y
Contrast enhancement gain 4 Y
Description (all gains limited to 0-255)
6
out
= (1/1)*(Yin-0) = Normal Contrast
5
threshold
out
out
out
out
out
out
out
= 1.235V). If the measured voltage is below this threshold
= (5/4)*(Y
= (9/8)*(Y
= (17/16)*(Y
= (17/16)*(Y
= (9/8)*(Y
= (5/4)*(Y
= (3/2)*(Y
4
in
in
in
in
in
-102) = Enhances Black
-57)
-0)
-0)
-0) = Enhances White
in
in
-30)
-0)
3
2
CE2
0
R/W
Symbol: CE
Address: 11H
Bits: 3
1
CE1
R/W
1
CH7008A
0
CE0
R/W
1
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