SEGA ST-V (SEGA Titan Video) MODBIOS

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Introduction

This project is for owners of a SEGA ST-V (SEGA Titan Video) PCB.

The ST-V is a cart based system which allows you to change game by changing a game cartridge. All cartridges are the same physically. There is no keyed connector protection like on the Taito F3 motherboard where a Japanese cart will only fit a Japanese motherboard.

On the ST-V it's the BIOS on the motherboard which controls the region selection. The following types of cart exist:

• Carts which work with all regions: Most carts.
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• Carts which work with all regions and change their in-game text according to the region selected: Soukyugurentai/Terra Diver is playable on all regions but in addition it will change the in-game text to English with an "English" BIOS.
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• Carts which work with all regions and change their gameplay depending on the region selected: Radiant Silvergun will only use two buttons if you play it with an USA or European BIOS!
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• Carts which contain the same game (albeit with different language) but which are locked to a specific region: Dynamite Deka and Die Hard Arcade are the same game, however Dynamite Deka will only work with a Japanese BIOS and Die Hard Arcade will only work with an "English" BIOS.
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• Carts which are locked to one region: Puyo Puyo Sun will only work with a Japanese BIOS. However Columns 97 will work with all BIOS's except USA!

Instead of buying an extra motherboard to make sure you can play all your games in the language you desire, you can just change the BIOS on the PCB.

Region selection

Inside each game cart there is region string. The string consists of 4 characters. The possible characters are:

• 'J' - Japan
• 'U' - USA
• 'E' - Europe
• 'T' - Taiwan

Inside the BIOS there is a region character (offset 0x809). It contains the letter 'J', 'U', 'E' or 'T'. When the PCB is powered the BIOS verifies that the region character can be found in the region string stored in the cart. Failure to find this will prevent the game from starting and a suitable error message will be displayed.

Changing the BIOS

One solution is to burn a copy of an alternate BIOS into a 27C400 EPROM. To save wear and tear on the chip socket you may want to buy a ZIF (Zero Insertion Force) socket as well.

Another solution is to burn two ROM images into an EPROM and then use a technique called bank switching to select between the two of them. This deprececated method is documented here for archival purposes ST-V (SEGA Titan Video) Dual BIOS

However the simplest solution is to use the ST-V MODBIOS created by the talented Joerg Hartenberger. With the ST-V MODBIOS all you need to do is to burn the image into a device equivalent to the one on your motherboard.

The ST-V MODBIOS

The ST-V MODBIOS has the following features:

• Very simple to use just select the region on power up
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• Defeats the country lockout (so that every game will work)
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• Allows you to select the region code (JP, EUR, US) for all games
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• The region code is stored in NVRAM making it persistent
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• Passes the memory test in the ST-V System Test Menu
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• Works with all ST-V motherboards

Parts

• An M27C400 EPROM or quivalent (AT 27C400 or MX27C4100). If your ST-V motherboard does not have a MASK ROM similar to the picture above you need to use the same EPROM as mounted on your PCB.
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• The ST-V MODBIOS image: epr-stv-multi_v111.zip

Procedure

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• Download the ST-V MODBIOS image and burn it into a suitable EPROM.
  
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• Replace IC8 on your PCB with the ST-V MODBIOS. If you don't have a proper EPROM extractor use a small screwdriver.
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• Power on the ST-V board and select the desired region using button A, B or C or do nothing to use the previously selected region.

ST-V Gamelist

Here is a list of ST-V games and which region they will operate in. This list is not a complete list of all ST-V games.

Disclaimer

I take no responsibility whatsoever for any damage you might cause to your hardware, yourself or your surroundings when making this BIOS.

"The future of ST-V rests upon our work and your work"
(Text found inside BIOS image)

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