★ HARDWARE Manual ★ VDP2 User's Manual ★ Chapter 2 TV screen
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VDP2 User's Manual / Chapter 2 TV Screen

■ 2.4 TV screen mode register

The TV screen mode register controls the display of the TV screen. It is a read / write 16-bit register located at address 180,000H. After turning on the power or resetting, the value will be cleared to 0, so be sure to set it.

TVMD 180000H
 15
 14
 13
 12
 11
 Ten
 09 09
 08 08
DISP --- --- --- --- --- --- BDCLMD

 07 07
 06 06
 05 05
 04
 03 03
 02 02
 01 01
 00
LSMD1 LSMD0 VRESO1 VRESO0 --- HRESO2 HRESO1 HRESO0

TV screen display bit : Display bit (DISP), bit 15
Controls the display of pictures on the TV screen.

 DISP
 process
 0
 Do not display pictures on TV screen
 1
 Display a picture on the TV screen

When this bit is 0, it is blank during the display period and VRAM access from the CPU or DMA controller is always possible.
The color displayed when this bit is 0 is specified by the BDCLMD bit.
Be sure to change this bit from 0 to 1 during the V blank period.

Border color mode bit : Border color mode bit (BDCLMD), bit 8
Controls the color displayed in the border area.

 BDCLMD
 process
 0
 Show black
 1
 Show back screen

When the DISP bit is 0, the color of the entire standard display area is specified. However, if this bit is set to 1 without setting the DISP bit to 1 even after the power is turned on or reset, the back screen will not be displayed correctly. If the back screen is set so that it can be specified for each line, the color displayed in the border area will be the same color as the bottom line in the setting display area.

Interlace mode bits : Interlace mode bits (LSMD1, LSMD0), bits 7, 6
Specifies the interlaced mode.

 LSMD1
 LSMD0
 process
 0
 0
 Non-interlaced
 0
 1
 Setting prohibited
 1
 0
 Monodense interlacing
 1
 1
 Dense interlace

Single-dense interlacing is a mode in which the same picture is displayed in odd-numbered and even-numbered fields, and double-dense interlacing is a mode in which different pictures are displayed in odd-numbered and even-numbered fields. In either case, there will be no gap between the scanning lines. Vertical resolution at double-dense interlaced 072 The vertical resolution is the same as at non-interlaced.
The picture displayed during double-dense interlacing is the vertical half of the picture displayed during non-interlaced or single-dense interlaced.
When the horizontal resolution (HRESO2 to HRESO0) is set to the dedicated monitor mode, be sure to set it to non-interlaced (00B).

Vertical resolution bits : Vertical resolution bits (VRESO1, VRESO0), bits 5, 4
Specifies the vertical resolution when displaying a picture on the TV screen.

 VRESO1
 VRESO0
 Vertical resolution
 Displayable monitor
 0
 0
 224 lines
 NTSC or PAL TV
 0
 1
 240 lines
 NTSC or PAL TV
 1
 0
 256 lines
 PAL TV
 1
 1
 Setting prohibited
 −

Increasing the vertical resolution adds an increment at the top and bottom of the screen, leaving the center of the screen unchanged.
If you set the horizontal resolution (HRESO2 to HRESO0) to dedicated monitor mode, this bit setting is ignored and fixed at 480 lines.

Horizontal resolution bits : Horizontal resolution bits (HRESO2 to HRESO0), bits 2 to 0
Specifies the horizontal resolution when displaying a picture on the TV screen.

 HRES02
 HRESO1
 HRESO0
 Horizontal resolution
 Graphic mode
 Displayable monitor
 0
 0
 0
 320 pixels
 Normal graphic A
 NTSC method or
 PAL TV
 0
 0
 1
 352 pixels
 Normal graphic B
 0
 1
 0
 640 pixels
 High resolution graphic A
 0
 1
 1
 704 pixels
 High resolution graphic B
 1
 0
 0
 320 pixels
 Dedicated normal graphic A
 31kHz monitor
 1
 0
 1
 352 pixels
 Dedicated normal graphic B
 High-definition monitor
 1
 1
 0
 640 pixels
 Dedicated high resolution graphic A
 31kHz monitor
 1
 1
 1
 704 pixels
 Dedicated high resolution graphic B
 High-definition monitor

Switching from normal graphic A (320 pixels) or high resolution A (640 pixels) to normal graphic B (352 pixels) or high resolution B (704 pixels) must be done during the horizontal return period. To comply with this limitation, be sure to use the service routine in the BOOT-ROM to switch the horizontal resolution.

If you specify Dedicated High-Resolution Graphic A or Dedicated High-Resolution Graphic B, you must set the other registers as determined. Refer to " Dedicated High-Resolution Graphic Mode " in " 2.1 TV Screen Mode".
Be sure to reset VDP2 when switching the TV screen mode from the dedicated monitor mode to the normal mode and high resolution mode.

caution
 Be sure to use the service routine in the BOOT ROM to switch the horizontal resolution.

There are restrictions on the combination of TV screen mode settings for VDP1 and VDP2. In addition, the screen display changes depending on the combination of interlace mode settings. Table 2.2 shows the restrictions on TV screen mode settings, and Table 2.3 shows the screen displays for each interlaced mode setting.

Table 2.2 Restrictions on TV screen mode settings
VDP2 setting (TVMD: HRESO2..0) VDP1 setting (TVMR: TVM2..0) Setting permission or disapproval
Normal mode
(000 or 001)		 Normal 000 Possible
High resolution 001 Setting prohibited
Rotation 16 010 Possible
Rotation 8 011 Possible
HDTV 100 Setting prohibited
High resolution mode
(010 or 011)		 Normal 000 Possible
High resolution 001 Possible
Rotation 16 010 Possible
Rotation 8 011 Possible
HDTV 100 Setting prohibited
Dedicated monitor mode
(100,101,110,111)		 Normal 000 Possible
High resolution 001 Setting prohibited
Rotation 16 010 Possible
Rotation 8 011 Possible
HDTV 100 Setting prohibited

Table 2.3 Screen display by interlace mode setting
LSMD value DIE value Display of VDP2 Display of VDP1
00 0 Non-interlaced Non-interlaced
1 Non-interlaced Cannot be displayed correctly
01 0 Monodense interlacing Monodense interlacing
1 Monodense interlacing Dense interlace
11 0 Dense interlace Monodense interlacing
1 Dense interlace Dense interlace
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★ HARDWARE Manual ★ VDP2 User's Manual ★ Chapter 2 TV screen
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