VDP Registers

Description

The VDP is programmed by setting registers.

With them you can enable/disable the display, setting address for the different planes etc ...

Setting registers is done by accessing the vdp control port.

Registers

0x0 - Mode set 1

Bit	7	6	5	4	3	2	1	0
Def	Unused set to 0			0 : Horizontal interrupt disabled 1 : Horizontal interrupt enabled	Unused set to 0	if not set to 1 display will be really dark	0 : Enable HV counter 1 : Disable HV Counter	Unused (0)

0x1 - Mode set 2

Bit	7	6	5	4	3	2	1	0
Def	Unused set to 0	0 : Display disabled 1 : Display enabled	0 : Vertical interrupt disabled 1 : Vertical interrupt enabled	0 : DMA disabled 1 : DMA enabled	0 : V28 CELL mode (always in NTSC) 1 : V30 CELL mode	Unused set to 1	Unused set to 0

0x2 - ScrollA adress

Bit	7	6	5	4	3	2	1	0
Def	0		A15-A13			0

Address will be XXX0_0000_0000_0000 (IE between 0x2000 and 0xE000)

The address can be 0x0.

0x3 - Window address

Bit	7	6	5	4	3	2	1	0
Def	0		A15-A11					0

In H40 CELL mode A11 must be 0.

Address will be XXXX_X000_0000_0000 (IE between 0x800 and 0xF800) in H32 CELL mode

Address will be XXXX_0000_0000_0000 (IE between 0x1000 and 0xF000) in H40 CELL mode

The address can be 0x0.

0x4 - ScrollB address

Bit	7	6	5	4	3	2	1	0
Def	0					A15-A13

Address will be XXX0_0000_0000_0000 (IE between 0x2000 and 0xE000)

The address can be 0x0.

0x5 - Sprites table address

Bit	7	6	5	4	3	2	1	0
Def	0	A15-A9

A9 must be 0 in H40 CELL mode

Address will be XXXX_XXX0_0000_0000 (IE between 0x200 and 0xFE00) in H32 mode

Address will be XXXX_XX00_0000_0000 (IE between 0x400 and 0xFC00) in H40 mode

0x7 - Background color

Select the color displayed in the background.

Bit	7	6	5	4	3	2	1	0
Def	0		Palette number		Color number

0xA - HINT

Set on how many lines HINT will occurs.

Bit	7	6	5	4	3	2	1	0
Def	number of lines

0xB - Mode set 3

Bit	7	6	5	4	3	2	1	0
Def	0				0 : Disable external interrupt 1 : Enable external interrupt	0 : Full VScroll mode 1 : Each 2 CELL VScroll mode	0 : Full HScroll mode 1 : Prohibited 2: Each 1 CELL HScroll mode 3: Each 1 line HScroll mode

See VDP_Scrolling.

0xC - Mode set 4

Bit	7	6	5	4	3	2	1	0
Def	0 : H32 CELL mode 1 : H40 CELL mode	0			0 : Disable Shadow / Highlight 1 : Enable Shadow / Highlight	0 : No interlace 1 : Interlace 2 : Prohibited 3 : Interlace (double resolution)		0 : H32 CELL mode 1 : H40 CELL mode

Bit 0 and 7 must be the same.

See VDP Interlace

0xD - HScroll table address

Bit	7	6	5	4	3	2	1	0
Def	0		A15-A10

Address will be XXXX_XX00_0000_0000 (IE between 0x400 and 0xFC00)

0xF - Auto increment

Bit	7	6	5	4	3	2	1	0
Def	auto increment

After each VRAM/CRAM/VSRAM access (read or write), the internal address will be incremented by this value.

0x10 - Scroll size

Bit	7	6	5	4	3	2	1	0
Def	0		0 : V32 CELL 1 : V64 CELL 2 : Prohibited 3 : V128 CELL		0		0 : H32 CELL 1 : H64 CELL 2 : Prohibited 3 : H128 CELL

This register apply to both ScrollA and ScrollB.

0x11 - Window horizontal position

Bit	7	6	5	4	3	2	1	0
Def	0 : Window is left from base point 1 : Window is right from base point	0		Base pointer value (in CELL)

0x12 - Window vertical position

Bit	7	6	5	4	3	2	1	0
Def	0 : Window is upper side from base point 1 : Window is lower side from base point	0		Base pointer value (in CELL)

0x13 - DMA counter low

Bit	7	6	5	4	3	2	1	0
Def	Lenght7-Lenght0

0x14 - DMA counter high

Bit	7	6	5	4	3	2	1	0
Def	Lenght15-Lenght8

0x15 - DMA source address low

Bit	7	6	5	4	3	2	1	0
Def	A8-A1

0x16 - DMA source address mid

Bit	7	6	5	4	3	2	1	0
Def	A16-A9

0x17 - DMA source address high

Bit	7	6	5	4	3	2	1	0
Def	0 : Memory to VRAM 1 : Depending of bit 6	When bit 7 is 0 : A23 When bit 7 is 1 : 0 : VRAM Fill 1 : VRAM Copy	A22-A17