Genesis Technical Overview

GENESIS: 

68000 @ 8 MHz 
Main CPU 
1 MByte ROM area 
64 KByte RAM area 
VDP (Video Display Processor) 
Dedicated video display processor 
Controls playfield & sprites 
Capable of DMA 
Horizontal & Vertical interrupts 
64 KByte of dedicated VRAM (Video RAM) 
64 x 9-bits of CRAM (Color RAM) 
Z80 @ 4 MHz 
Controls PSG (Programmable Sound Generator) 
8 KByte of dedicated sound RAM 


VIDEO: 

NOTE: Playfield and Sprites are character-based •Display Area (visual) 
40 chars wide x 28 chars high 
Each char is 8 x 8 pixels 
Pixel resolution is 320 x 224 (NTSC) 
3 planes 
2 scrolling playfields 
1 sprite plane 
Definable priorities between planes 
Playfields 
Each char position takes 2 bytes, that includes: 
Char name (10 bits); points to char definition 
Horizontal flip 
Verical flip 
Color palette (2 bits); index into CRAM •Priority 
Scrolling 
1 pixel scrolling resolution •Horizontal 
Whole playfield as unit •Each character line •Each scan line 
Vertical: 
Whole playfield as unit 
2 char wide columns 


Sprites 
1 x 1 char up to 4 x 4 chars 
Up to 80 sprites can be defined 
Up to 20 sprites displayed on a scan line 
Sprite priorities 
Character definitions 
4 bits/pixel; points to color register 
4 bytes/scanline of char 
32 bytes for complete char definition 
Playfield & sprite chars are the same! 



COLOR: 

Uses CRAM (part of the VDP) 
64 9-bit wide color registers 
3 bits of Red •3 bits of Green •3 bits of Blue 
4 palettes of 16 colors 
0th color (of each palette) is always transparent 



OTHER: 

DMA 
Removes the 68000 from the BUS 
Can move 205 bytes/scanline during VBLANK 
There are 36 scanlines during VBLANK 
DMA can move 7380 bytes during VBLANK 

Horizontal & Vertical interrupts 

SOUND: 

Z80 controls 
PSG chip (TI 76489) 
FM chip (Yamaha YM 2612) 
6-channel stereo 
Z80 can access ROM data 
8 KByte RAM 


© 1996 Damaged Cybernetics