ch7004c Chrontel, ch7004c Datasheet - Page 12

• Manufacturer Part Number: ch7004c
• Description: Digital Pc To Tv Encoder With Macrovisiontm
• Manufacturer: Chrontel

CHRONTEL
4.3.3 Display Modes
The CH7004 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 output to either
NTSC or PAL television formats. The CH7004 provides interpolated 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 ovescan
of 10%. (Negative values) indicate modes which are operating in underscan.
The inclusion of multiple levels of scaling for each resolution have been created to enable optimal use of the
CH7004 for different application needs. In general, underscan (modes where percent overscan is negative provides
an image that is viewable in its entirety on screen; it should be used as the default for most applications (e.g.,
viewing text screens, operating games, running productivity applications and working within Windows).
Overscanning provides an image that extends past the edges of the TV screen, exactly like normal television
programs and movies appear on TV, and is only recommended for viewing movies or video clips coming from the
computer. In addition to the above mode table, the CH7004 also support interlaced input modes, both in CCIR 656
and proprietary formats (see Display Mode Register section.)
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Table 11. CH7004 Display Modes
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
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
28.196
30.210
39.273
43.636
47.832
21.147
26.434
30.210
23.790
29.455
20.140
24.671
21.000
26.250
31.500
29.500
36.000
39.000
25.000
31.500
28.125
34.875
21.000
26.250
Clock
Pixel
201-0000-024 Rev. 2.4, 6/24/2004
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
CH7004C
Vertical
Total
525
750
420
525
600
420
525
420
525
500
625
750
625
750
836
500
625
500
625
500
625
600
630
630
700