ST-V (SEGA Titan Video) Dual BIOS

Written by Tormod Tjaberg

Last update: 2006-09-05

Image of Dual BIOS chip

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 just inserting another 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:

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 region string consists of 4 characters. The possible characters are:

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.

An even simpler 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.

Note:
If your ST-V mother board is equipped with an EPROM of type 27C4096 (or equivalent) you cannot make a dual BIOS. The reason for this is that the 4 Mbit (256K x 16-Bit) EPROM is not available in 8Mbit. The only solution is to buy a ZIF socket, burn the alternate BIOS image into another 27C4096 and switch manually.

Bank Switching

The ST-V BIOS image is 524288 (0x80000) bytes long. This means that one needs 18 address lines to address the entire image. If one has 19 address lines one can address 1048576 (0x100000) bytes or twice the amount of memory.

The following drawing shows two images which are stored in memory of a 27C800 EPROM. This device is capable of storing 1Mbit or 1048576 bytes of data.

Image of 27C800 memory map

By using 18 address lines we can address up to 0x080000 i.e the Image Of Letter A image. By using 19 address lines and setting the topmost bit (A18) to 0 we can still only address 0x080000 bytes. If we set the topmost bit (A18) to 1 we will start accessing the Image Of Letter B image and this image only!

This technique is called bank switching. By changing the address of the upper address bit we will effectivly switch banks. By storing two BIOS images in a 27C800 EPROM we can switch between them by setting address line A18 high or low.

So in order to get a dual BIOS all you need to do is to concatenate two BIOS images, burn them to a suitable EPROM and install a simple switch.

To determine which BIOS images to burn you might want to compare the list below against the games you own.

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.

Game Region code
ASTRA SUPERSTARS J
BAKU BAKU ANIMAL J
BATMAN FOREVER JUE
COLUMNS97 JTE
COTTON2 JUET
COTTON_BOOMERANG JUET
DANCHI HANAFUDA J
DECATHLETE JTUE
DIE HARD ARCADE UET
DYNAMITE DEKA J
EJIHON J
ELANDOREE JTUE
F.FIGHT REVENGE JUET
FINAL ARCH J
FIND LOVE J
FUNKYHEAD BOXERS JTUE
GOLDEN AXE DUEL JTUE
GROOVE ON FIGHT J
GUARDIAN_FORCE JUET
HANAGUMI COLUMNS J
INTRO DON DON J
KIWAMES J
MARUCHAN DE GOO J
OJAMA THE WORLD J
OTHELLO SHIYOUYO J
PEBBLEBEACH GOLF JUE
PRO_WRESTLING_FV J
PURIKURA SAKUSEN J
PUYO PUYO SUN J J
RADIANT.S.GUN JUET
SANDO-R J
SASI-SU!! J
SEABASS FISHING JUET
SHANGHAI BANRI JUE
SHIENRYU JTUE
SOKYU GURENTAI JUET
SPORT FISHING 2 J
SPORT FISHING 2 UET
SSS JUET
SUIKO ENBU JUET
SUPER M.LEAGUE U
TREASURE HUNT UETJ
V.F REMIX JTUE
V.F. KIDS JTUE
VIRTUAL MAJONG J
VIRTUAL MAJONG2 J
WINTERHEAT JTUE
WORLD CUP'98 JTUE

The only game on this list which requires an USA BIOS is "Super Major League".

Requirements

Disclaimer

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

If you don't have the expertise to make your own dual BIOS, you can order one from JammaBoards.

Note:
I do not sell or manufacture these ST-V Dual BIOS's. So please don't ask me to make or sell you one.

BIOS Images

Image of ST-V Mask Chip

Here is a list of all the known ST-V BIOS images and their CRC32's:

Filename CRC32 Description
epr19730.ic8 0xd0e0889d Japan
mp17951a.s 0x2672f9d8 Japan (Alt)
20091.bin 0x59ed40f4 Japan (Alt 2)
mp17952a.s 0xd1be2adf USA
mp17953a.ic8 0xa4c47570 Taiwan
mp17954a.s 0xf7722da3 Europe

Procedure


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


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