SEGA Mega Drive Technical Details and Trivia

Connectors

  • Cartridge port
  • 2 x controller ports (9-pin D-subminiature)
  • EXT input port - an expansion port on first-model Japanese units and early USA and European units (9-pin female D-connector) - used for the Japanese 'Meganet' modem.
  • Power connector - Model 1 used a 2.1mm barrel connector with negative tip. Model 2 used an EIAJ-03 coaxial connector with positive tip. Both need 9-10V, but Model 1 draws more current at 1.2A. The Model 2 draws 0.85 amps.
  • Expansion port - edge connector on side, used almost exclusively for connection of a Mega CD/Sega CD. The port was removed on the Genesis 3 model.
  • Headphone jack - provides stereo audio output. Only present on Model 1.
  • RF output - (RCA jack) only present on Model 1.
  • A/V output - provides both RGB and Composite video output, and audio output (Model 1 = 8-pin DIN with mono audio output, Model 2 = 9-pin Mini-DIN with stereo audio output).

     

Technical Facts

  • The 32X add-on came with twin Hitachi SH2 32-bit RISC processors running at 23 MHz, a further 512K of RAM, allowed up to 32,768 colours on-screen simultaneously with 50,000 polygons per second, a stereo PCM audio chip in combination with the existing 12 channels in the standard unit.
  • The 8-pin A/V port on the Model 1 Mega Drive is the same as that used by the Sega Master System.
  • The Mega Drive had more board revisions and cosmetic versions produced than any other console. There are 3 'models' (Model 1, Model 2 and Model 3), each with a number of board variants. You can easily identify the different Model and Board variants using the table at the bottom of this page and cross-referencing it to the silk screen identification at the bottom of the Mega Drive board:
  • European Mega Drives cannot play Japanese games because the PAL Mega Drive has a slightly different cartridge slot shape - this means the larger Japanese cartridges won't physically fit into a PAL Mega Drive. Adapters were sold to enable this. No other restrictions exist, e.g. regional encoding, on the PAL Mega Drive. PAL Mega Drives can play almost all Genesis games without any adapter, however Genesis owners require an adapter to play Mega Drive games. For Japanese Mega Drives, they did implement region-encoding technology in software (TMSS, or TradeMark Security System), but adoption of this was left to the games developer. Konami usually made use of it on their titles, whilst Electronic Arts largely ignored it altogether. The Japanese version of Namco's Rolling Thunder 2 was apparently the first region-encoded Mega Drive game to be region-locked.
  • Brazilian Mega Drives cannot play European or Japanese cartridges due to a region encoding restriction. All Brazilian Mega Drives were manufactured and distributed by Tec Toy, a toymaker.
  • The Mega Drive can only address up to 4MB of game at any one time, meaning under normal circumstances, Mega Drive games are limited to a maximum size of 4MB (or 32 megabits as was more commonly advertised). This is increased, however, using a technique known as bank switching - hardware built into the cartridge which allows "banks" of memory to be "switched" at run time. As an example, the first half of a game might be loaded into memory when the console is turned on, and when a certain condition is met, the second half is loaded in, replacing the first half (how this is achieved depends on how the game is programmed). Bank switching in dedicated video game consoles dates back to at least the Atari 2600, however it was not implemented in Mega Drive titles until the mid-1990s, as for the most part, cartridge space was not considered an issue for developers (or at least, not enough of one to justify the extra cost implementing a bankswitching system, and for many years the Sega Mega-CD was a viable option too).
  • You can identify the Japanese Mega Drive compared to the European model because the Japanese version has red labelling below the "16-BIT" logo where the power LED is, and the reset button is blue. On the European model the labelling is white and the reset button is white/light grey.
  • Brazilian models can be distinguished by having the text 'HIGH DEFINITION GRAPHICS' in a semi-circle at the top of the console.
  • One interesting feature of Japanese cartridges is a inclusion of a cartridge "lock", which prevents the cartridge from being removed when the system turns on. A plastic piece from the system is slid across to a gap on the left hand side of a Japanese cartridge, securing it in place when the power switch is moved (similar tricks can be found on the Super NES and the TurboGrafx-16). This locking mechanism is only present in Japanese Model 1 Mega Drives and is absent in all western models - the vast majority of Western cartridges lack the gap required for cartridge locking, with exceptions being the likes of "special" cartridges, e.g. Sonic & Knuckles.

 

Hover your mouse over the circuit board for a description of the components

Model 1 Variant 6 board

 

 

Trivia

  • A total of 31 cartridge-based games and 5 Sega CD-based games supported the 32X add-on. Most of these were written by Sega, or were colour-enhanced versions of existing titles.
  • At the time of releasing the 32X add-on, no games were available that could use it. Instead, Sega offered coupons to buyers for future 32X games!
  • A common myth is that the Mega Drive II did not come with the Zilog Z80. If this was true most games would not be able to produce sound, as this second processor was often used to generate sound as well as provide the ability to play Master System games. All Mega Drive II came with a Z80 second processor, but depending on the board revision these were manufactured by other companies who had a licensing agreement with Zilog. In later revisions of the Mega Drive II board, the Z80 was integrated into a custom ASIC which also included other major chips on the board.
  • If a game designed for an NTSC unit (Genesis) is run on a PAL machine (Mega Drive), the difference in refresh rate means the game will run 17.5% slower and will have extra horizontal borders surrounding the top and bottom of the image. Knowing this, some developers (particularly those based in Europe) chose to optimise their games for PAL regions, typically by speeding up the music and gameplay. On rare cases this also meant utilising the extra 16 rows of pixels that PAL provides over NTSC.
  • Unlike newer consoles such as the Sega Dreamcast, the Mega Drive does not natively support any PAL60 modes. It is not, however, uncommon to see modified hardware to circumvent these issues.

 

Model number and Board revisions:

Model Board Variant (VA) Silk Screen ID Description
1 VA0  

CPU = 68000-based Hitachi-made HD68HC000.
Seperate I/O chips: SEGA 315-5308, 315-5309, and 315-5345 (DIP-16 packages)
Motorola 68K memory = 2 x TC51832SPL-12
Z80 CPU = Zilog Z084004PSC
Z80 memory = NEC D4168C-15 (8K x 8)

1 VA1    
1 VA2 IC BD M5 USA VA2 837-6992 Video encoder chip = Sony CXA1145P
1 VA3    
1 VA4 IC BD M5 PAL VA4  
1 VA5    
1 VA6 IC BD M5 USA
(or)
IC BD M5 PAL
Seperate I/O chips consolidated into a single package - SEGA 315-5433.
Video encoder chip = 9237
1 VA6.8    
1 VA7 PC BD M5 USA VA7  
2 VA0 PC BD MD2 VA0 PAL CPU = Motorola-branded MC68HC000.
VDP and I/O chips consolidated into a single ASIC: SEGA 315-5660
Video encoder chip = KA2195D or CXA1145M or MB3514
2 VA1    
2 VA1.8 PC BD MD2 VA1.8 PAL
(or)
PC BD MD2 VA1.8 ASIA
 
2 VA2    
2 VA2.3    
2 VA3 PC BD MD2 VA3 USA HAL  
2 VA4    
3 VA1   Main ASIC (SEGA 315-6123) now incorporates 68000 CPU, Z80 CPU, VDP, and YM2612 audio chip)
Memory now consolidated also into a single 128Kx16 SDRAM.
Sony CXA1645M replaces CXA1145 as video encoder chip.
3 VA2