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sega genesis mega drive vdp register reference · bit-level breakdown · all 24 registers · dma · scroll planes · sprite table · shadow highlight · runs locally

enter register number (0–23) — click any row in the table to jump to it

R#0 — Mode Register 1

Controls HV latch, H-interrupt, display mode, and column clipping.

value (hex)00000000VDP cmd: $80 $00

bitsnamecurrent valuedescription

7unused0 ($00)always 0

6unused0 ($00)always 0

5M50 ($00)Mode 5 (Genesis mode): 1 = Genesis VDP mode (must be 1 for normal operation)

4IE10 ($00)H-interrupt enable: 1 = generate interrupt when H-interrupt counter reaches 0

3LCB0 ($00)Left column blank: 1 = force leftmost 8 pixels black (hides horizontal scroll artifact)

2HVLATCH0 ($00)HV counter latch enable: 1 = latch H/V counter when /HL pin is asserted

1unused0 ($00)always 0

0unused0 ($00)always 0

all registers

R#00Mode Register 1

R#01Mode Register 2

R#02Plane A Scroll Table Base

R#03Window Plane Base

R#04Plane B Scroll Table Base

R#05Sprite Table Base

R#06Sprite Pattern Base (SMS only)

R#07Background Color

R#08Horizontal Scroll (SMS mode)

R#09Vertical Scroll (SMS mode)

R#10H-Interrupt Counter

R#11Mode Register 3

R#12Mode Register 4

R#13H-Scroll Table Base

R#14Nametable Pattern Base (SMS)

R#15Auto-Increment

R#16Scroll Plane Size

R#17Window H Position

R#18Window V Position

R#19DMA Counter (Low)

R#20DMA Counter (High)

R#21DMA Source (Low)

R#22DMA Source (Mid)

R#23DMA Source (High) + Type

vdp i/o port map ($C00000–$C00013)

$C00000R/WData portRead/write VRAM, CRAM, or VSRAM data (16-bit word; auto-increments address by R#15)

$C00002R/WData port mirrorMirror of $C00000

$C00004R/WControl portW: VDP command word (VRAM addr, register write, DMA trigger). R: VDP status register

$C00006R/WControl mirrorMirror of $C00004

$C00008RH counterCurrent horizontal beam counter (9 bits, top 8 returned — tracks dots/line)

$C0000ARV counterCurrent vertical beam counter (tracks scanline)

$C00011WPSG dataWrite to SN76489 PSG (4-channel square wave + noise — also at $C00013)