Chapter 2 TV screen

■ 2.1 TV screen mode

VDP2 can display images on NTSC and PAL TVs, 31kHz monitors and HDTV monitors. There are three types of TV screen modes for displaying images: normal mode, high resolution mode, and dedicated monitor mode. The screen scanning method can be selected from three types: non-interlaced, single-dense interlaced, and double-dense interlaced. There is also a register that shows the scanning status of the TV.
Table 2.1 shows the TV screen modes and graphic modes that can be selected and the resolutions at that time.
Special settings are required to specify the dedicated high-resolution graphic A and the dedicated high-resolution graphic B.

Table 2.1 TV screen modes

TV screen mode	Graphic mode	Interlaced mode	Resolution Horizontal x Vertical (pixels)	Restrictions on use
normal	Normal graphic A	Non-interlaced	320 x 224
			320 x 240
			320 x 256	For PAL method only
		Interlace	320 x 448
			320 x 480
			320 x 512	For PAL method only
	Normal graphic B	Non-interlaced	352 x 224
			352 x 240
			352 x 256	For PAL method only
		Interlace	352 x 448
			352 x 480
			352 x 512	For PAL method only
High resolution	High resolution graphic A	Non-interlaced	640 x 224
			640 x 240
			640 x 256	For PAL method only
		Interlace	640 x 448
			640 x 480
			640 x 512	For PAL method only
	High resolution graphic B	Non-interlaced	704 x 224
			704 x 240
			704 x 256	For PAL method only
		Interlace	704 x 448
			704 x 480
			704 x 512	For PAL method only
Dedicated monitor	Dedicated normal graphic A	Non-interlaced	320 x 480	For 31kHz monitor only
	Dedicated normal graphic B	Non-interlaced	352 x 480	For high-definition monitors only
	Dedicated high resolution graphic A	Non-interlaced	640 x 480	For 31kHz monitor only
	Dedicated high resolution graphic B	Non-interlaced	704 x 480	For high-definition monitors only

● High resolution mode

The precautions when the TV screen mode is set to high resolution mode are as follows.

• The normal scroll surface (NBG0 to NBG3) is displayed as if the picture when the TV screen mode is in normal mode is reduced to 1/2 in the horizontal direction.

• The rotating scroll surface (RBG0,1) can be displayed, but the horizontal resolution of the picture is the same as when the TV screen mode is normal mode.

• The VRAM cycle pattern register is valid only for T0 to T3, and invalid for T4 to T7.

• The vertical cell scroll function cannot be used.

• The color calculation function is limited. For details, refer to "12.1 Color Calculation Function".

• The extended color calculation function and the blur calculation function cannot be used.

● Dedicated high resolution graphic mode

The graphic mode of the dedicated high resolution graphic A or the dedicated high resolution graphic B displays one side by combining the two sides of NBG0 and NBG1. In that case, the correct display cannot be performed unless the following settings are made.

• Make only NBG0 and NBG1 visible.

• Use exactly the same data for the NBG0 and NBG1 character pattern tables (or bitmap patterns) and pattern name tables.

• Allow both NBG0 and NBG1 to be reduced horizontally to 1/2.

• Set the same vertical screen scroll value for NBG0 and NBG1.

• Set the horizontal screen scroll value of NBG1 to be 1 larger than the horizontal screen scroll value of NBG0.

• Set both NBG0 and NBG1 horizontal coordinate increments to 2.

• Set the color RAM mode to mode 0.

• Set the same value for the priority numbers of NBG0 and NBG1.

• Do not insert the line color screen.

• Both NBG0 and NBG1 special priorities should be in mode 0.

• Do not use the color calculation function.

• For each register other than the above, make the same settings for NBG0 and NBG1.