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★ 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. This is a 16-bit readable and writable register located at address 180000H. The value is cleared to 0 after power-on or reset, so be sure to set it.

TVMD 180000H
   15   
   14   
   13   
   12   
   11   
   10   
   09   
   08
DISP - - - - - - BDCLMD

   07   
   06   
   05   
   04   
   03   
   02   
   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 the TV screen
 1
 Display a picture on the TV screen

When this bit is 0, it remains blank during the display period, allowing VRAM access from the CPU or DMA controller at any time.
The color displayed when this bit is 0 is determined 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
 display black
 1
 Display back screen

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

Interlace mode bit : Interlace mode bit (LSMD1, LSMD0), bits 7, 6
Specify interlaced mode.

 LSMD1
 LSMD0
 process
 0
 0
 non-interlaced
 0
 1
 Setting prohibited
 1
 0
 Single dense interlace
 1
 1
 double dense interlace

Single dense interlace is a mode in which the same picture is displayed in odd and even fields, and double dense interlace is a mode in which different pictures are displayed in odd and even fields. In either case, there will be no gaps between scan lines. Vertical resolution 072 during double-dense interlacing The vertical resolution is the same as when non-interlaced.
The picture displayed during double-dense interlacing is vertically 1/2 times the picture displayed during non-interlacing or single-dense interlacing.
When setting the horizontal resolution (HRESO2 to HRESO0) to dedicated monitor mode, be sure to set it to non-interlace (00B).

Vertical resolution bit : Vertical resolution bit (VRESO1, VRESO0), bits 5, 4
Specify the vertical resolution when displaying pictures on the TV screen.

 VRESO1
 VRESO0
 vertical resolution
 Viewable 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
 −

Increments when increasing vertical resolution are added to the top and bottom of the screen; the center of the screen remains unchanged.
If the horizontal resolution (HRESO2 to HRESO0) is set to dedicated monitor mode, this bit setting will be ignored and fixed at 480 lines.

Horizontal resolution bit : Horizontal resolution bit (HRESO2 to HRESO0), bits 2 to 0
Specify the horizontal resolution when displaying pictures on the TV screen.

 HRES02
 HRESO1
 HRESO0
 horizontal resolution
 graphic mode
 It can be displayed
 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
 HD monitor
 1
 1
 0
 640 pixels
 Dedicated high resolution
 Graphic A
 31kHz monitor
 1
 1
 1
 704 pixels
 Dedicated high resolution
 Graphic B
 HD monitor

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

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

Note
 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. Also, the screen display changes depending on the combination of interlace mode settings. Table 2.2 shows the limitations of TV screen mode settings, and Table 2.3 shows the respective screen displays depending on the interlace mode settings.

Table 2.2 Restrictions on TV screen mode settings
VDP2 settings (TVMD:HRESO2..0) VDP1 settings (TVMR:TVM2..0) Setting permission/denial
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 depending on interlace mode setting
LSMD value DIE value VDP2 display VDP1 display
00 0 non-interlaced non-interlaced
1 non-interlaced cannot be displayed correctly
01 0 Single dense interlace Single dense interlace
1 Single dense interlace double dense interlace
11 0 double dense interlace Single dense interlace
1 double dense interlace double dense interlace
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★ HARDWARE Manual ★ VDP2 User's Manual ★ Chapter 2 TV Screen
Copyright SEGA ENTERPRISES, LTD., 1997