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