Difference between revisions of "Sega MegaDrive"

From SizeCoding
Jump to: navigation, search
Line 1: Line 1:
 
== SEGA MegaDrive / Genesis ==
 
== SEGA MegaDrive / Genesis ==
−
The Sinclair QL (for Quantum Leap) is a personal computer launched by Sinclair Research in 1984, as an upper-end counterpart to the ZX Spectrum.
+
The SEGA MegaDrive / Genesis is a 16-bit videogame console released by SEGA in 1989.
−
It was aimed at the serious home user and professional and executive users markets from small to medium-sized businesses and higher educational establishments, but failed to achieve commercial success.
+
 
−
The Sinclair QL uses a Motorola 68008.CPU with 32-bit internal data registers, but an 8-bit external data bus.
+
It features:
 +
- 320x240 resolution (PAL)
 +
- 4x 16 color palettes
 +
- Tile based display chip with 2 scrolling tilemaps
 +
- 64 Sprites (up to 4x4tiles in size each)
 +
- 64K of dedicated Video Memory (VRAM)
 +
- YM2612 Sound Chip
  
 
=== Setting up ===
 
=== Setting up ===
Line 84: Line 90:
 
dc.l  INT_Null ; Unused (reserved)
 
dc.l  INT_Null ; Unused (reserved)
 
</syntaxhighlight>
 
</syntaxhighlight>
 +
This vector table is then followed by the ROM header at 0x100
  
 
=== ROM Header ===
 
=== ROM Header ===
−
The ROM Header is a structure that specifies some metadata about the ROM, like its name, author, version number, release date, region,
+
The ROM Header is a structure located at 0x100 that specifies some metadata about the ROM, like its name, author, version number, release date, region, and any special peripherals used.
−
and any special peripherals used.
 
  
 
Note that the Mega Drive console itself doesn't read any of this, it's more a convenience for the programmer, but most emulators will read the title and region. Further header information at: https://plutiedev.com/rom-header
 
Note that the Mega Drive console itself doesn't read any of this, it's more a convenience for the programmer, but most emulators will read the title and region. Further header information at: https://plutiedev.com/rom-header

Revision as of 16:42, 18 December 2025

SEGA MegaDrive / Genesis

The SEGA MegaDrive / Genesis is a 16-bit videogame console released by SEGA in 1989.

It features: - 320x240 resolution (PAL) - 4x 16 color palettes - Tile based display chip with 2 scrolling tilemaps - 64 Sprites (up to 4x4tiles in size each) - 64K of dedicated Video Memory (VRAM) - YM2612 Sound Chip

Setting up

The real hardware and BlastEm emulator don't require exact ROM headers, but you might want to distribute an emulator friendly version of your production as well for broader emulator compatibility.

CPU Vector table

This must be the very first thing in the ROM, since the CPU reads it from 0x0000 on bootup. The Vector table is a table of addresses that the CPU needs to know about - things like stack address, "main()" function address, vertical/horizontal interrupt addresses, etc. For any interrupts we don't want to handle, we specify INT_Null (an interrupt at the bottom of the file that doesn't do anything). 

        dc.l   0x00FFE000			; Initial stack pointer value
	dc.l   CPU_EntryPoint		; Start of program
	dc.l   CPU_Exception 		; Bus error
	dc.l   CPU_Exception 		; Address error
	dc.l   CPU_Exception 		; Illegal instruction
	dc.l   CPU_Exception 		; Division by zero
	dc.l   CPU_Exception 		; CHK CPU_Exception
	dc.l   CPU_Exception 		; TRAPV CPU_Exception
	dc.l   CPU_Exception 		; Privilege violation
	dc.l   INT_Null				; TRACE exception
	dc.l   INT_Null				; Line-A emulator
	dc.l   INT_Null				; Line-F emulator
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Spurious exception
	dc.l   INT_Null				; IRQ level 1
	dc.l   INT_Null				; IRQ level 2
	dc.l   INT_Null				; IRQ level 3
	dc.l   INT_HInterrupt		; IRQ level 4 (horizontal retrace interrupt)
	dc.l   INT_Null  			; IRQ level 5
	dc.l   INT_VInterrupt		; IRQ level 6 (vertical retrace interrupt)
	dc.l   INT_Null				; IRQ level 7
	dc.l   INT_Null				; TRAP #00 exception
	dc.l   INT_Null				; TRAP #01 exception
	dc.l   INT_Null				; TRAP #02 exception
	dc.l   INT_Null				; TRAP #03 exception
	dc.l   INT_Null				; TRAP #04 exception
	dc.l   INT_Null				; TRAP #05 exception
	dc.l   INT_Null				; TRAP #06 exception
	dc.l   INT_Null				; TRAP #07 exception
	dc.l   INT_Null				; TRAP #08 exception
	dc.l   INT_Null				; TRAP #09 exception
	dc.l   INT_Null				; TRAP #10 exception
	dc.l   INT_Null				; TRAP #11 exception
	dc.l   INT_Null				; TRAP #12 exception
	dc.l   INT_Null				; TRAP #13 exception
	dc.l   INT_Null				; TRAP #14 exception
	dc.l   INT_Null				; TRAP #15 exception
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)
	dc.l   INT_Null				; Unused (reserved)

This vector table is then followed by the ROM header at 0x100

ROM Header

The ROM Header is a structure located at 0x100 that specifies some metadata about the ROM, like its name, author, version number, release date, region, and any special peripherals used.

Note that the Mega Drive console itself doesn't read any of this, it's more a convenience for the programmer, but most emulators will read the title and region. Further header information at: https://plutiedev.com/rom-header

Memory map



Video display


To be added.



VDP


To be added.



 to be added


Sprites


To be added



; to be added


Sound


To be added.



; to be added


Additional Resources







					

						Retrieved from "http://www.sizecoding.org/index.php?title=Sega_MegaDrive&oldid=1873"