Mega Drive

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Revision as of 09:18, 9 September 2011 by SuperEgg (talk) (Model 2)
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Fast Facts on the Sega Mega Drive

Made by: Sega
Variants: Mega Drive 2, Genesis 3, Sega Mega Jet, Sega Nomad, Sega Teradrive
Processor: Motorola 68000 (or equivalent), 7.67MHz NTSC/7.61MHz PAL; Zilog Z80 (or equivalent) for sound programming and Master System compatibility, 3.58MHz NTSC/3.55MHz PAL
Released in US: 9 January 1989
Released in EU: Winter 1990
Released in JP: 29 October 1988

The Sega Mega Drive, or Sega "Genesis" as it is called in the United States is a 4th Generation Home video game console produced by Sega. It was introduced to the market in 1989 as competition to rival Nintendo's Super Nintendo Console.

The Mega Drive is a Video Game console that is based mainly for home use. During it's run, Sega had three models released (while the last model was not produced by Sega, but by another company unde license) and each one becoming smaller than the original. The system ran through an A/V out cable that connected to a television. The console itself boasted one of the fastest processors in it's time, The Motorolla 68000 series. This chipset was attributed to making the Mega Drive run at such high speeds without lag that most processors of its time would crash from the amounts of instructions being sent to be processed. Along with it, it also came equipped with a Zilog Z80 chip that handled sound and music processing for the console. With all of this running inside, the Mega Drive was one of the first game console to boast of having 16-bit music and art, and to top it off, the Genesis had "Blast Processing," which was not much other than a marketing slogan.

Model 1 and Model 2 Mega Drives have an expansion port for the Sega CD peripheral. In addition to the Sega CD, in 1995 Sega released the 32x peripheral. This piece of equipment was to be placed directly into cartidge slot, and enhanced the console with two 32-bit CPUs and increased audio and video capabilities.

Hardware Revisions

Model 1

An early Model 1 Sega Genesis.

Model 1 is the original release of the system in 1988. This version was released in all regions. The only differnces between the two versions is that the American Release had "Genesis" printed on it as apposed to "Mega Drive"

Basic Features

The outputs on the back of the Model 1 Genesis.
  • Two Controller ports
  • A/V out ports
  • The system had the switch that selected which channel the RF Signal would be picked up on
  • Capabilities to play up to 4 MB (more with special cartridges) games
  • Stereo sound output only through headphone port
  • EXT port on the back of the console, used mostly for the Mega Modem
  • Larger circuit board and less distorted sound output
A sample of the Mega Drive's sound capability.

The Model 1 Mega Drive can easily be identified by the large rectangular shape, and the non-distorted audio. The Model 1 Mega Drive also came bundled with the original Sonic the Hedgehog, and it very popular along console modders due to the large motherboard. A model 1 Genesis can also be identified by it's FCC ID - if it is FJ846EUSASEGA or FJ846EUSASEGA you can usually be sure that you have a Model 1 at hand. Some Model 1's also used some sort of Motorola 68000 clone instead of the official CPU from Motorola.

Model 2

Sega eventually released a later version of the Mega Drive dubbed the "Mega Drive 2" or Model 2. It featured a smaller more square appearance, removed the headphone jack, volume slider, as well as the 'EXT' port in the back of the console. Sega also changed the DIN plug at the back of the console to 9 pins to be able to output stereo sound. The Back had a much simplier design, only having the standard A/V out port and Power adapter input.
The outputs on the back of the Model 2 Genesis.

Programming the Mega Drive

Programming games and software for the Mega Drive is no easy task. The following information is intended to provide you some help while doing so.

Memory Map

Start address End address Description
$000000 $3FFFFF Cartridge ROM/RAM
$400000 $7FFFFF Reserved (used by the Sega CD and 32X)
$800000 $9FFFFF Reserved (used by the 32X)
$A00000 $A0FFFF Z80 addressing space
$A10000 $A10001 Version register (read-only word-long)
$A10002 $A10003 Controller 1 data
$A10004 $A10005 Controller 2 data
$A10006 $A10007 Expansion port data
$A10008 $A10009 Controller 1 control
$A1000A $A1000B Controller 2 control
$A1000C $A1000D Expansion port control
$A1000E $A1000F Controller 1 serial transmit
$A10010 $A10011 Controller 1 serial receive
$A10012 $A10013 Controller 1 serial control
$A10014 $A10015 Controller 2 serial transmit
$A10016 $A10017 Controller 2 serial receive
$A10018 $A10019 Controller 2 serial control
$A1001A $A1001B Expansion port serial transmit
$A1001C $A1001D Expansion port serial receive
$A1001E $A1001F Expansion port serial control
$A10020 $A10FFF Reserved
$A11000 Memory mode register
$A11002 $A110FF Reserved
$A11100 $A11101 Z80 bus request
$A11102 $A111FF Reserved
$A11200 $A11201 Z80 reset
$A11202 $A13FFF Reserved
$A14000 $A14003 TMSS register
$A14004 $BFFFFF Reserved
$C00000 $C00001 VDP data
$C00002 $C00003 VDP data (mirror)
$C00004 $C00005 VDP control
$C00006 $C00007 VDP control (mirror)
$C00008 $C00009 VDP HV counter
$C0000A $C00010 Reserved
$C00011 PSG input
$C00012 $FEFFFF Reserved
$FF0000 $FFFFFF M68k RAM