Chapter 2 TV screen

■2.1 TV screen mode

VDP2 can display images on NTSC and PAL TVs, 31kHz monitors, and high-definition monitors. There are three TV screen modes for displaying images: normal mode, high resolution mode, and dedicated monitor mode. You can choose from three types of screen scanning: non-interlace, single-density interlace, and double-density interlace. There is also a register that indicates the TV's scanning status.
Table 2.1 shows the TV screen modes and graphic modes that can be selected and their resolutions.
Please note that special settings are required when specifying dedicated high resolution graphic A and dedicated high resolution graphic B.

Table 2.1 TV screen mode

TV screen mode	graphic mode	interlace mode	resolution Width x height (pixels)	Restrictions on use
normal	normal Graphic A	non-interlaced	320×224
			320×240
			320×256	For PAL method only
		interlace	320×448
			320×480
			320×512	For PAL method only
	normal Graphic B	non-interlaced	352×224
			352×240
			352×256	For PAL method only
		interlace	352×448
			352×480
			352×512	For PAL method only
high resolution	high resolution Graphic A	non-interlaced	640×224
			640×240
			640×256	For PAL method only
		interlace	640×448
			640×480
			640×512	For PAL method only
	high resolution Graphic B	non-interlaced	704×224
			704×240
			704×256	For PAL method only
		interlace	704×448
			704×480
			704×512	For PAL method only
dedicated monitor	dedicated normal Graphic A	non-interlaced	320×480	For 31kHz monitor only
	dedicated normal Graphic B	non-interlaced	352×480	For high-definition monitors only
	Dedicated high resolution Graphic A	non-interlaced	640×480	For 31kHz monitor only
	Dedicated high resolution Graphic B	non-interlaced	704×480	For high-definition monitors only

●High resolution mode

Please note the following when setting the TV screen mode to high resolution mode.

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

• The rotating scroll surface (RBG0, 1) can be displayed, but the horizontal resolution of the picture will be 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.

• Vertical cell scrolling function cannot be used.

• Color calculation functions will be limited. For details, see " 12.1 Color calculation function ."

• Extended color calculation function and blurring calculation function cannot be used.

●Dedicated high resolution graphic mode

In the graphics mode of dedicated high-resolution graphic A or dedicated high-resolution graphic B, two sides of NBG0 and NBG1 are combined to display one screen. In that case, correct display will not be possible unless the following settings are made.

• Please make only NBG0 and NBG1 visible.

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

• Please make it possible to reduce both NBG0 and NBG1 to 1/2 horizontally.

• Set the vertical screen scroll value of NBG0 and NBG1 to be the same.

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

• Set the horizontal coordinate increment of both NBG0 and NBG1 to 2.

• Set the color RAM mode to mode 0.

• Set the same priority number for NBG0 and NBG1.

• Do not insert line color screens.

• Set the special priority of NBG0 and NBG1 to mode 0 for both.

• Do not use color calculation functions.

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