ch7006c Chrontel, ch7006c Datasheet - Page 11

• Manufacturer Part Number: ch7006c
• Description: Ch7006 Digital Pc To Tv Encoder
• Manufacturer: Chrontel

CHRONTEL
4.3.2 Color Burst Generation*
The CH7006 allows the subcarrier frequency to be accurately generated from a 14.31818 MHz crystal oscillator,
leaving the subcarrier frequency independent of the sampling rate. As a result, the CH7006 may be used with any
VGA chip (with an appropriate digital interface) since the CH7006 subcarrier frequency can be generated without
being dependent on the precise pixel rates of VGA controllers. This feature is a significant benefit, since even a
± 0.01% subcarrier frequency variation may be enough to cause some television monitors to lose color lock.
In addition, the CH7006 has the capability to genlock the color burst signal to the VGA horizontal sync frequency,
which enables a fully synchronous system between the graphics controller and the television. When genlocked, the
CH7006 can also stop “dot crawl” motion (for composite mode operation in NTSC modes) to eliminate the
annoyance of moving borders. Both of these features are under programmable control through the register set.
4.3.3 Display Modes
The CH7006 display mode is controlled by three independent factors: input resolution, TV format, and scale factor,
which are programmed via the display mode register. It is designed to accept input resolutions of 640x480,
800x600, 640x400 (including 320x200 scan-doubled output), 720x400, and 512x384.
It is designed to support
scaling with selectable factors of 5:4, 1:1, 7:8, 5:6, 3:4 and 7:10 in order to support adjustable overscan or underscan
operation when displayed on a TV. This combination of factors results in a matrix of useful operating modes which
are listed in detail in Table 11.
(1) Note: Percent underscan is a calculated value based on average viewable lines on each TV format, assuming an average TV over-
scan of 10%. (Negative values) indicate modes which are operating in underscan.
Table 11. CH7006 Display Modes
201-0000-026 Rev. 2.8, 6/24/2004
TV Format
Standard
NTSC
NTSC
NTSC
NTSC
NTSC
NTSC
NTSC
NTSC
NTSC
NTSC
NTSC
NTSC
NTSC
PAL
PAL
PAL
PAL
PAL
PAL
PAL
PAL
PAL
PAL
PAL
PAL
For NTSC: 480 active lines - 10% (overscan) = 432 viewable lines (average)
For PAL: 576 active lines - 10% (overscan) = 518 viewable lines (average)
Resolution
(active)
640x480
640x480
640x480
800x600
800x600
800x600
640x400
640x400
640x400
720x400
720x400
512x384
512x384
640x480
640x480
640x480
800x600
800x600
800x600
640x400
640x400
720x400
720x400
512x384
512x384
Input
output to either NTSC or PAL television formats. The CH7005 provides interpolated
Factor
Scale
7:10
1:1
7:8
5:6
5:6
3:4
5:4
1:1
7:8
5:4
1:1
5:4
1:1
5:4
1:1
5:6
1:1
5:6
3:4
5:4
1:1
5:4
1:1
5:4
1:1
TV Lines
Active
480
420
400
500
450
420
500
400
350
500
400
480
384
600
480
400
600
500
450
500
400
500
400
480
384
Percent (1)
Overscan
(19%)
(29%)
(15%)
(29%)
(29%)
(35%)
(11%)
(3%)
(8%)
(3%)
(8%)
(8%)
(8%)
(4%)
(4%)
(4%)
(8%)
10%
16%
16%
16%
10%
14%
14%
4%
24.671
Clock
24.671
28.196
30.210
39.273
43.636
47.832
21.147
26.434
30.210
23.790
29.455
20.140
21.000
26.250
31.500
29.500
36.000
39.000
25.000
31.500
28.125
34.875
21.000
26.250
Pixel
Horizontal
Total
1040
1040
1064
1000
1008
1125
1116
784
784
800
840
840
840
945
936
800
784
840
840
840
944
960
936
840
840
CH7006C
Vertical
Total
525
600
630
630
700
750
420
525
600
420
525
420
525
500
625
750
625
750
836
500
625
500
625
500
625
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