ch7007a Chrontel, ch7007a Datasheet - Page 30

• Manufacturer Part Number: ch7007a
• Description: Ch7007a Digital Pc To Tv Encoder
• Manufacturer: Chrontel

CHRONTEL
Connection Detect Register
The Connection Detect Register provides a means to sense the connection of a TV to either S-Video or Composite
video outputs. The status bits, YT, CT, and CVBST correspond to the DAC outputs for S-Video (Y and C outputs)
and Composite video (CVBS), respectively. However, the values contained in these status bits are NOT VALID
until a sensing procedure is performed. Use of this register requires a sequence of events to enable the sensing of
outputs, then reading out the applicable status bits. The detection sequence works as follows:
1. Ensure the power management register bits 2-0 are set to 011 (normal mode).
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 CH7007, 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].
30
Bit:
Symbol:
Type:
Default:
Bit:
Symbol:
Type:
Default:
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
7
6
6
5
5
threshold
= 1.235V). If the measured voltage is below this threshold
4
4
3
YT
R
X
3
201-0000-002
2
CT
R
X
2
CE2
0
R/W
Symbol: CDR
Address: 10H
Bits: 4
Symbol: CE
Address: 11H
Bits: 3
1
CVBST
R
X
1
CE1
R/W
1
Rev. 2.95, 6/24/2004
CH7007A
0
SENSE
W
0
0
CE0
R/W
1