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 at $C00008 and 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

VDP Ports

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