VDP Ports

Data port

The Data port is at 0xC00000 or $C00002 and is used for reading/writing to the VRAM,CRAM or VSRAM.

You first have to select the address and RAM using the control port.

Bit	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Def	D15-D0

Control Port

The control port is at $C00004 or $C00006 (only for writing).

Read

Reading it will get the status register.

Bit	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Def	Nothing						0 : 1 : FIFO empty	0 : 1 : FIFO full	0 : 1 : V interrupt happened	0 : No sprites overflow 1 : Sprites overflow	0 : No collision 1 : Collision between two sprites	0 : Even frame 1 : Odd frame (in interlace mode)	0 : Not in VBLANK 1 : In VBLANK	0 : Not in HBLANK 1 : In HBLANK	0 : DMA not busy 1 : DMA busy	0 : NTSC mode 1 : PAL mode

Writing to it can be done for setting registers or setting RAM address for further read/write.

Write 1 - Setting Register

Bit	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Def	always 1	always 0		Register number					Register value

Write 2 - Setting RAM address

First word

Bit	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Def	CD1-CD0		A13-A0

Second word

Bit	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Def	0								CD5-CD2				0		A15-A14

CD0-CD5 select the address mode.

Access mode	CD5	CD4	CD3	CD2	CD1	CD0
VRAM Write	0	0	0	0	0	1
CRAM Write	0	0	0	0	1	1
VSRAM Write	0	0	0	1	0	1
VRAM Read	0	0	0	0	0	0
CRAM Read	0	0	1	0	0	0
VSRAM Read	0	0	0	1	0	0

CD4 and CD5 are used while doing DMA access.

HV Counter

The HV counter port is used to read the current line/frame drawn by the VDP.

Non interlace mode

Bit	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Def	Frame number								Line number

Interlace mode

Bit	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
Def	VC7	VC6	VC5	VC4	VC3	VC2	VC1	VC8	Line number