Adding Switches to your Mega Drive
Well, theres my switched Mega Drive - damn, it looks good! Notice the switches at the bottom left, just next to the volume control. It is possible to play any game from any region on this console. Follow these instructions to make your Mega Drive / Genesis multi-region - regardless its country of origin. Note that this guide is only intended for use with the original model 1 Mega Drive1.

What you Need

You will need the following: 1. A screwdriver 2. Some long wire 3. A soldering iron 4. Solder 5. A sharp knife 6. Two SPDT switches 7. An RGB SCART lead
Figure 2.1: Mega Drive ipped upside down. Note that
the six screws holding the machine together are located around the perimeter of the case.

Figure 2.2:

Mega Drive opened in the correct manner, with no strain being put on the "power on" LED.
Opening up your Mega Drive
First of all, turn your Mega Drive upside down (as in Figure 2.1), and unscrew the six screws on the bottom of the machine. Now turn your Mega Drive over such that it is in the normal playing position, and slowly lift the top casing as shown in Figure 2.2. Be careful of the wires that connect to the red "power on" LED. To disconnect the wires, simply bend the LED legs so theyre straight, and pull the connector o. When it comes to reconnecting the LED, note that one LED leg is longer than the other - the red wire attaches to the longer leg. Alternatively, you could write R[ed] and W[hite] next to the legs - its inside the case so its not like anyone will see it. Bear in mind that your Mega Drive wont have the red wires shown at the left hand side of Figure 2.2 (yet). Now unscrew the screws that hold down the shielding. Dont forget about the gold screw on top! NOTE: Once youve nished, remember to put the shielding and casing back to the way they were! Be sure to match up the "on" switch and the volume control on the casing with their corresponding parts on the circuit board when putting the upper casing back on. Once the shielding is removed, you should see something similar to Figure 2.3 (minus the extra red wires, of course!). Youre now ready to perform the modication.

JP1 JP2

JP3 JP4

Figure 2.6: Japanese.

Figure 2.7: English.

Figure 2.8: 60Hz NTSC.

Figure 2.9: 50Hz PAL.

Building the Switches

In the following diagrams, the red dashed lines represent wires and each three-pronged hub at the bottom represents a switch. To make things clearer, please refer to sections 2.4.1 and 2.4.2, respectively.

Japanese

English

60Hz (NTSC)

50Hz (PAL)
Figure 2.10: Language Switch.
Figure 2.11: Frequency Switch.

Language Switch

Take a SPDT switch and a piece of wire. Solder one end of the wire to point "3" and the other to the middle connection of the switch. Now take another piece of wire and solder one end to point "2" and the other to the left connection of the switch. Finally take another piece of wire and solder one end to point "4" and the
other to the right connection of the switch, giving something which looks similar to Figure 2.10. Voila - you have your language switch! 2.4.2 50Hz / 60Hz Switch
Take another SPDT switch and a piece of wire. Solder one end of the wire to point "5" and the other to the middle connection of the switch. Now take another piece of wire and solder one end to point "6" and the other to the left connection of the switch. Take another piece of wire and solder one end to point "8" and the other to the right connection of the switch, as in Figure 2.11. Now you have a 50Hz/60Hz switch. It is worth noting here that if you are modifying a PAL console, the 60Hz output given by this switch is not true NTSC (for more information on this, see the FAQs in Section 3). All this means is that you will need to use an RGB SCART lead in order to play your games in colour (in 60Hz mode).2 This works the other way as well - if its an NTSC system that you are modifying, you will need an RGB SCART for games to play in colour while in 50Hz mode.

Fitting the Switches

This part is entirely your choice. You can see what I did, and personally I cant think of a better place to t the switches. By popular demand, the following describes exactly how I went about tting switches to the Mega Drive pictured above: I used two miniature SPDT [Single Pole, Double Throw] mounting slide switches. Most people use SPDT toggle switches, but I tend to prefer the overall look of the slide switches used here (they dont stick out much, making them rather neat and unobtrusive). To actually t one of the switches, I drilled a small hole on the side of my Mega Drive [after hours of measuring/debating], making sure that the hole would be smaller than the head of the switch. I then led away, constantly checking to see whether or not the switch would comfortably slide from one position to the other. Once I had a good, neat (and straight) t, I marked the position of the xing holes and drilled a tiny hole through each of the aforementioned markings. Its then just a matter of screwing the switch into place. The second switch is tted in exactly the same way, but be sure to measure everything out relative to the rst switch if you want them to be neatly aligned. You might want to put masking tape over the area of casing you intend to drill through before marking/drilling, as this can help prevent the drill from slipping.

Failure to use an RGB SCART lead will result in the game playing in black and white. Apparently, some television sets are able to cope with the signal that the Mega Drive outputs when it is being played in the wrong frequency setting, but in most cases you will need an RGB SCART to play the game in colour.
Widening the Cartridge Slot
Ahhh. you thought you were nished - didnt you? Well, youre not - theres still one last thing to do. It turns out that Japanese Mega Drive cartridges are wider than non-Japanese Mega Drive cartridges. Here, Ive used Thunder Force IV 3 as an example:
Notice how the European cart has those little notches at either side (at the back) whereas the Japanese cart is curved. Well, you guessed it, those sleek Japanese carts just dont t into non-Japanese Mega Drives. The reason is that Sega cunningly changed the shape of the Euro/US carts and the shape of the cartridge slot on the console, so as to prevent people importing from Japan. This is easily rectied by simply dismantling the cartridge slot on the Mega Drive and ling down the little notches on each side. Once you have your console open, youll see some screws holding the cartridge mechanism together - unscrew them. Now look for the protruding "corners" at either side of the slot, and take them o. I used a fret-saw to get rid of the majority of the edge, and then led the rest until a Japanese cart would t. Make sure you get a good clean t, with plenty of space for a cart to t in without any scratches - after all, once everythings back together the cart slot will look almost exactly the same as it did before (from the outside, at least). Sunsoft 4 cartridges are probably the best to use for testing the width of the slot, as they are the widest of all Japanese Mega Drive carts. Then screw everything back together, and your Mega Drive will be able to accept Japanese games! Japanese systems also have trouble accepting non-Japanese cartridges due to a cartridge lock that holds the game in the cart slot while the system is switched on. You see that little slot at the side of the Japanese cart? Thats where the piece of plastic slides in to prevent the game being pulled out while the Mega Drive is switched on (a very clever and useful device, I must say). To x this, all you have to do is remove the lock on the inside of the Mega Drive by removing the screw that holds it in place. Then screw everything back together, and your Japanese Mega Drive will be able to accept non-Japanese games. NOTE: DO NOT le the game carts themselves! Apart from potentially destroying the game, the cart will look terrible, and is guaranteed to be worthless - no one likes buying led carts.

Congratulations!

You can now play Import Mega Drive games! Simply switch to "60Hz" and "Japanese" for Japanese mode, "60Hz" and "English" for US mode, and "50Hz" and "English" for European mode.
There are many interesting dierences between the European release and the Japanese releases of this game. First, the developers call themselves Technosoft in the Euro version and Tecno Soft in the Japanese version. Secondly, the 100 lives cheat doesnt work in the Japanese version - instead, you start with 0 lives! 4 The following are Sunsoft games: TEL TEL Mahjong, Batman, TEL TEL Baseball Staduim, Shi Kin Joh, Super Fantasy Zone, Lemmings, Flashback and Panorama Cotton.
Frequently Asked Questions
Why do I need to make my Mega Drive multi-region?
If you want to play the majority of Japanese (and American) import games, your only options are to either buy a bridge adapter or to perform a hardware modication on your Mega Drive. The former merely allows the Japanese cartridges to t into your Mega Drive, and wont allow you to play all import games (Japanese or American). The latter will allow you to play ANY Mega Drive game, regardless of where it was released.
Why are some Mega Drive games locked out?
In order to answer this question, well have to go through a brief history of the Mega Drive. The Mega Drive was originally released in Japan, then in the USA (with the name changed from Mega Drive to Genesis), and lastly in Europe (where it was called Mega Drive again). Now, Sega was (and still is) split up into three main divisions - Sega Japan, Sega of America, and Sega Europe - and each of these divisions work independently of one another. This means that if European Mega Drive owners had imported all of their games from America, Sega Europe would have made no money, and the Mega Drive would have been discontinued in Europe. With the Mega Drive ocially discontinued in Europe, there would have been no TV ads, no Mega Drive magazines, and no awareness of the Mega Drive for most of the European public. As most games were released in Japan and America before they were released in Europe (and since the games-playing public are a pretty impatient bunch), importing was a popular way of buying games. So Sega introduced the lock-out system.

How does the lock-out system work?
Without going into too much detail, heres a quick outline of the three major gaming territories: Region Japan USA Europe TV Signal 60Hz NTSC 60Hz NTSC 50Hz PAL Language Japanese English English
So a Japanese game could be programmed to run if and only if the console has a Japanese language setting (i.e. Japanese games will only play on a Japanese Mega Drive). Similarly, an American game could be programmed to run if and only if the console has an English language setting AND a 60Hz NTSC signal. Likewise, European games could be programmed to run if and only if the console has an English language setting AND a 50Hz PAL signal.
What is a bridge adapter, how does it work, and why doesnt it allow me to play all import games?
A bridge adapter just acts as a bridge to allow Japanese Mega Drive games to t into a non-Japanese Mega Drive. If you look at a Japanese cartridge, you will see that it is not the same shape as a European or US cartridge. Due to the dierence in shape, a Japanese Mega Drive cartridge will not t into a non-Japanese Mega Drive (unless the cartridge slot is widened). So if a Japanese game has no in-built security, it will play on a non-Japanese Mega Drive provided you can physically t the cart into the slot. As mentioned earlier, though, some games are programmed to recognise the territory of the console on which they are playing, and
so a bridge adapter will only allow you to play some Japanese games. Bridge adapters do NOT make your console play games in 60Hz mode.
What is a Universal Adapter ?
Universal adapters (such as the one released by Datel) are becoming increasingly hard to nd these days, and are often confused with bridge adapters. Like a bridge adapter, the universal adapter is placed between the game and the console. However, a universal adapter will always contain several DIP switches which allow you to select the region of the game you wish to play, and the label on the cartridge will explain which switch settings are to be used for each region. However, a universal adapter does not make a European/Asian Mega Drive output 60Hz.
What about the Game Genie / Pro Action Replay?
Both the Game Genie (Galoob) and the Pro Action Replay (Datel) are cheat cartridges, designed to let the user hack into the game of their choice and alter parameters which control various aspects of the game. This means that such a device can be used, for example, to give the user innite lives, unlimited energy, access to hidden levels, and control of the game speed. Due to the nature of these devices, codes may be "invented" for just about any game, with many bizarre (and game-enhancing) results - such as the ability to execute special moves in mid-air for the Street Fighter II series. The devices use lock-on technology (similar to the bridge adapter and the universal adapter), meaning that the cheat cartridge plugs into the Mega Drive with the game plugged directly on top of the cheat cartridge. As such, both the Game Genie and the various incarnations of the Pro Action Replay may be used as a bridge adapter for foreign games. However, many people have noticed that these devices have a distinct advantage over simple bridge adapters, namely that by entering specic region-free codes an import game can be forced to run on a domestic console. Unfortunately, each game requires a dierent code in order to play in a specic territory, and so there is no universal code which works for all games. Furthermore, I must point out that a large number of games do not currently have region-free codes available for use with cheat cartridges, and that codes are not compatible between dierent devices (i.e. a region-free code which works with the Pro Action Replay will not work with the Game Genie). In short, this option only works if someone has invented a code for the particular game you wish to play and the cheat cartridge you intend to use. However there are a couple of documents in the "Genesis Hardware FAQs" section of GameFAQs which list a large number of region-free game codes, so if you already have one of these devices you should denitely check these out. As in the previous cases, a Game Genie / Pro Action Replay will not make a European Mega Drive output 60Hz.

Whats the big deal with 50Hz PAL?
OK, lets break this down. First, well deal with the PAL issue. In Europe (and some areas of Japan), PAL is the standard television signal. In the USA and Japan, NTSC is the standard television signal. PAL was developed after NTSC, and is, believe it or not, the superior of the two systems - PAL uses more horizontal lines (312 lines compared to 262) for each frame, hence a higher resolution. The reason why the majority of gamers complain about PAL is for one simple reason - most games are developed in the USA and Japan,
where NTSC is the standard, and so most games are optimised for the NTSC system. So the 262 lines used for each frame of game play are squished in the middle of the 312 lines used by a PAL television. This means that PAL games have bars at the top and bottom of the screen, and it also means that the graphics look crushed:

Sonic the Hedgehog (PAL)

Sonic the Hedgehog (NTSC)
As can be seen from the above screenshots, Sonic looks like a dwarf in PAL mode! So thats why most Europeans dont like PAL when playing our Mega Drive games. Now for the 50Hz issue. In 50Hz mode we have 25 frames per second, while in 60Hz mode we have 30 frames per second. So a game running in 60Hz mode is 20% faster than it is running in 50Hz mode. What this means (in Mega Drive lingo) is that Sonic runs 20% faster in 60Hz than he does in 50Hz - and believe me, thats a lot! You can really feel the dierence when playing your favourite game in a dierent frequency setting; 50Hz feels incredibly slow and sluggish, while 60Hz feels fast and slick. Again, with 50Hz being the standard in Europe and 60Hz the standard in the US and Japan, most games were designed to be played in 60Hz mode - which means that the European Mega Drive gamers suer again. As you can see, its really two separate problems that European (and Australian) Mega Drive players have to deal with here.
Why is my picture black and white?
Due to the fact that the main crystal of a PAL Mega Drive is marginally dierent from the main crystal of an NTSC Mega Drive, the output of a switched PAL Mega Drive (in 60Hz mode) is almost (but not quite) an NTSC signal. In order to x this, you must use an RGB SCART lead. Here is a Usenet post from Mike G explaining how it works:
>Coming to think of it right now, there is something on the board that looks like a >crystal or whatever, Its got 53.20342 MHz on it. Not exactly pal or ntsc standard but anyway. Thats the main crystal. This frequency has to be divided by integer numbers to produce the main clock frequency and (in the Mega Drive) the colour subcarrier frequency. (Thats why its such an odd value and not, say, 50MHz.) 53.203425MHz divided by 12 gives 4.433619MHz, which is the exact colour subcarrier frequency required for PAL. In a NTSC Mega Drive, the main crystal is 53.693175MHz. Dividing this by 15, you end up with 3.579545MHz, which is the subcarrier frequency for NTSC. This discrepancy results

in the CPU in NTSC MDs running at a slightly faster clock speed, but not so much that youd notice! The frequency is divided by 12 or 15 depending on what the 50/60Hz jumper/pin is set to. This means that if you have a PAL MD set to 60Hz or a NTSC MD set to 50Hz, the colour subcarrier is at the "wrong" frequency (hence you need a RGB SCART cable when playing games at 60Hz on a European MD, otherwise you get a black-and-white picture). None of the above is relevant for the Mega PC, actually (because it doesnt use a composite or RF connection, so doesnt need a colour subcarrier), but I just thought Id mention it :-) -Mike
Why am I experiencing slowdown in 60Hz NTSC mode?
As many gamers will attest, some sections of games are notorious for slowing down when theres a lot of action going on. This is because the CPU cant process the game information quickly enough to run the game at full speed. In 60Hz mode slowdown is generally more prominent than it is in 50Hz mode. European gamers may remember some slowdown when playing (usually when one player loses lots of rings). Well in 60Hz this the game is running faster in the rst place. It is important to not experience more slowdown than an unmodied US Genesis that matter. Sonic the Hedgehog 2 in two-player mode slowdown is slightly more noticeable, since note that a modied PAL Mega Drive will or an unmodied Japanese Mega Drive, for
Is there any way to minimise (or, even better, eliminate) slowdown?
Yes, there is a way of doing this. Apparently, Sega underclocked the Motorola 68000 (the Mega Drives core processor) to run at 7.67MHz. The reasons behind this are unknown (possibly to prevent overheating or premature parts failure?), but people have found ways of overclocking the processor to reduce lag and allow even the most slowdown-ridden games to play without a hitch. The Mega Drives processor has been forced to run at speeds of up to 16MHz while maintaining stability (contrary to popular belief, overclocking a Mega Drive does not cause its games to run faster than their intended speed). Note that overclocking will require a separate modication and, for most people, the eort involved isnt really worth it. However, the hobbyists among you should denitely check out Epic Gamings website at http://www.bluespheer.com/host/epicgaming//md oc/ for information on the procedure involved. Please note that overclocking is not covered in this guide and is completely separate from making your Mega Drive multi-region. I cannot answer any questions regarding overclocking - although Im happy to hear from anyone who has successfully overclocked their console.
Can I play locked out European games in 60Hz NTSC mode?
Yes, you can. Once you have performed the modication, set your Mega Drive to 50Hz PAL English mode, and at any time after the SEGA logo has appeared switch the frequency to 60Hz. In most games, you will be able to play the game at its intended speed. In some games, however, the music will be out of sync (PAL Cool Spot, for example) or there will be some graphical glitches at certain points of the game (as in the PAL versions of Alien Soldier, Virtua Racing, Another World and Gunstar Heroes).

I plugged one of my English games into a Japanese Mega Drive, and it now plays in Japanese - why?
Many early Mega Drive games were burned onto what is called a dual-language ROM. Take the European release of Streets of Rage II, for example. If you play it on its intended console (that is, a European Mega Drive) itll work as expected, with all of the text in English. However, plug the exact same cart into a Japanese Mega Drive and youll nd yourself playing Bare Knuckle II, the Japanese version of Streets of Rage II, which has almost all of its text in Japanese (plus a few other cool dierences: "Skate" is renamed "Sammy", Mr X now smokes a cigar on the nal stage. etc). So, how did the same game change languages simply by plugging it into a dierent machine? Because the European release of Streets of Rage II contains exactly the same ROM as the Japanese release, and the game was simply programmed to recognize a European machine from a Japanese one - the console determines which version of the game is run. So someone living in the UK could buy Bare Knuckle II, plug it into their European PAL Mega Drive (after the appropriate cartridge slot modication), and it would magically play in English. Other games which feature this characteristic include Quackshot, GhoulsN Ghosts and Gauntlet IV. Note that the console does not translate anything; sort of like a magic act, the trick was carried out well before anyone knew what to look for - in this case, the trick was performed at the factory where the ROM was burned. Another interesting point is that the dual-language in Streets of Rage II only works between European and Japanese consoles (when set to US mode, the European release of Streets of Rage II gives the usual message explaining that you need either a PAL or a Japanese Mega Drive).
Which games use lock-out technology?
Any game released prior to 1992 will run on a Mega Drive of any region. However, there is no easy way of determining which import games released during and after 1992 are playable on a domestic console. To add even more confusion, just because a game is region-free in one territory does not mean that it is unprotected in another - for example, the US release of some games will play on any [unmodied] console, whilst the corresponding European release may only run on a European Mega Drive (and so on). This means that the only way of being sure of which games are locked out is to test each one. The "Territory Lock-out List" on the "Genesis Hardware FAQs" section of GameFAQs attempts to list which games contain a territory lock-out, and is worth checking out.
Is it true that widening the cartridge slot makes my console multi-region?
No. The cartridge modication allows Japanese games to physically t into a non-Japanese Mega Drive, but it does not allow locked out games to play.

I heard that the very rst run of Mega Drive consoles had no region lockout. Is this true?
No. All Genesis / Mega Drive consoles block protected import games by default. There are no exceptions.
Is there any way to make my Mega Drive change its region automatically?
There is no known way of modifying a Genesis / Mega Drive to automatically switch its region depending on which game is inserted. Im inclined to believe that it would be impossible to do this, since there are a
number of dual-language games out there. For example, the Japanese and European releases of Streets of Rage 2 use exactly the same ROM - so how would an auto-switching console know which region to choose? It would either crash, or ignore one of the language-settings altogether (e.g. Bare Knuckle 2 - the Japanese version of Streets of Rage 2 - may be impossible to play on such a machine).
Is there such a thing as a lock-out chip ?
There is no such thing as a lock-out chip in Genesis / Mega Drive games. Territorial lock-out is performed in the form of software, and is therefore eectively PART of the game. When a protected cart is inserted, the rst thing the game does is check the console on which it is being run such that it can determine what to do next. For example, say we insert a Japanese game which uses territorial lockout (such as Monster World IV) into a non-Japanese (unmodied) console: 1. First, the game checks the console to determine which region it is from. 2. If the console has the same conguration as a Japanese Mega Drive, the game will then load - otherwise, the game will refuse to load and will instead display a pre-programmed warning message. As you can see, theres no point including an expensive chip to prevent importers playing games when simply adding a tiny (eectively free) amount of code to the game would do the trick.
What about the licensing screen which appears upon powering up the console?
This is the famous Mega Drive Boot-ROM. Later revisions of the model 1 console (those manufactured after February 1991, I believe) introduced a licensing check to prevent companies from releasing unlicensed games (as opposed to territorial lockout, which is used to prevent people from importing games). As such, original model 1 systems are able to play some of the early [and unlicensed] Accolade games. The story goes something like this: Basically, Accolade [under the Ballistic alias] and Electronic Arts [neither of which were ocial Sega licensees] decided to reverse-engineer some ocial Mega Drive / Genesis games in the hope of learning how to write their own games. At one point, some apparently meaningless code was found near the beginning of each reverse-engineered game (i.e. it served no purpose - when removed, the games loaded and played as expected), so they decided not to include this code in their games. A huge court battle between Sega and Accolade ensued and, in the end, Segas later board revisions of the model 1 Mega Drive / Genesis included a check for the omitted "ocial" code to disable the unlicensed releases. Assuming we are attempting to play a protected game, the order in which these two [completely independent] procedures work is as follows: 1. First, the console scans the game to determine whether or not it may be run. 2. Then the game checks the console to determine whether or not that specic console may run the game. Do not confuse the ability to play unlicensed games with the ability to play region locked games! For example, games which checks the frequency of the console before loading (such as PAL Alien Soldier) will refuse to load on a US Genesis - regardless of its model. I have found that consoles with "high denition graphics and stereo sound" printed on the rim of the

disc surrounding the cartridge slot and an "EXT" port on the back are the only ones which might not display the licensing screen (unfortunately, the last batch of consoles to use this "old-style" case also included a license-test). If anyone knows a better method of identifying license-free machines, please let me know.
My modied Mega Drive / Genesis has slightly dierent jumper connections to those outlined in the guide, yet it still works. Why?
The guide is based around the way I modied my Mega Drive - and the set-up shown will work when applied to a Mega Drive of any region (US, Europe, or Japan). However, there are slightly dierent set-ups that also work perfectly well. Galen Tatsuo Komatsu neatly demonstrates this using his modied Genesis. The console was modied in such a way that it has one switch for each jumper, and after a couple of tests he came up with the following tables:

Language

JP1 open open closed closed JP2 open closed open closed output English English Japanese *short*

50Hz/60Hz

JP3 open open closed closed JP4 open closed open closed output 60Hz 60Hz 50Hz *short*
As you can see, selecting two conicting states simultaneously (i.e. "English and Japanese" or "50Hz and 60Hz") results in the power line being connected directly to the ground line and the console fails to power up. It is also worth pointing out that "English" and "60Hz" appear to be the dominant settings. So on this console we could have wired it such that our language switch connects across JP1 when switched to one position, and is open when icked to the other. Referring to the diagram in Section 2.3 we could have, for example, "1" wired to the middle connection, "2" wired to the right connection, and leave the left connection open. Similarly, our 50Hz/60Hz switch could have been wired such that we have JP3 closed in one position, and open in the other. I believe the modication would have also worked if we had used "1" and "7" as the central connections for our language and frequency switches respectively, since "1" is soldered to "3", and "5" to "7" on the backside of the board. NOTE: I strongly recommend you stick to the original settings used in Section 2, as these have been thoroughly checked and better explained.
Why are the printed traces on my Genesis dierent from the "US" setting shown in the guide?
The printed traces on a US Genesis go across JP2 and JP4 (thats 3-4 and 7-8 in the diagram). As explained in the above answer, points "5" and "7" are are already connected - so end result is the same. In short, just stick to the guide and youll be ne! For the record, the printed traces on a PAL Mega Drive go across JP2 and JP3, and on a Japanese Mega Drive they go across JP1 and JP4.
On my board, JP1 and JP2 are in a dierent area from JP3 and JP4. How do I modify this console?

This will not aect the modication procedure. JP1 and JP2 control the language of the console, and work independently of JP3 and JP4 (which control the output frequency [50/60]Hz). So instead of wiring both switches to the lower-right section of the circuit board, simply wire one switch to the section in which JP1 and JP2 are located, and the other to the area in which JP3 and JP4 are located.
My board has a capacitor across one of the four jumpers. How do I proceed?
On some of the older boards you may nd a capacitor on one jumper (usually one of the language jumpers). If you have a capacitor here, note that it is on the unused jumper for your consoles region - for example, on an English-language console the capacitor will be across JP1. It has been determined that this serves no purpose, and so its completely safe to de-solder the capacitor at either end (i.e. remove it). You can now use Section 2 of this guide to modify your console. NOTE: Thanks to Carlo Savorelli and Lorenzo Nocentini for risking their Mega Drive to verify this.
Does modifying my console allow me to play any Sega/Mega CD game?
As far as unmodied consoles go, you cannot pick and mix Sega/Mega CD and Genesis/Mega Drive systems. A US Genesis will only work with a US Sega CD. The Sega CD (US version of the Mega CD) needs a US Genesis in order to function - it simply wont work with a foreign console. Of course, with switches installed on your base Mega Drive (or Genesis) you can get round this by switching to US-mode before loading a Sega CD game. As for playing Mega CD (that is, European or Japanese) games on a US Sega CD, you need a converter cartridge such as the Pro CD-X released by Datel in the UK. This plugs into the cartridge slot of your system, allowing games from the selected region to play on your Sega CD - you dont need switches on your system to play Jap CD games if youre using a US Sega CD. The downside? You cant have a back-up RAM cart and an import converter in your system at the same time - so games that rely on a RAM cart, like Japanese Shining Force CD, are pretty much out of the question. Note that you cant switch your Mega Drive to Japanese mode to play a Japanese CD game on your US Sega CD, as the two systems would think they are from dierent regions - and the Sega CD wouldnt work. You need an adapter to force two systems from dierent regions to work with one another. If you live in Europe and wish to play import CD games on your European Mega CD, youve got an extra hurdle to overcome - namely the dreaded 50/60Hz problem. When you load an import game using the Datel adapter on a European Mega CD, things generally work OK until you reach FMV-heavy sections of the game (in fact, the CD audio works independently of the game speed, and so all CD audio will be out-of-sync with the graphics). Now I havent tried this myself (as I dont have a Mega CD), but I believe it should be possible to play imports on a modied European Mega Drive by switching to 60Hz, plugging in the Pro CD-X adapter, and then loading the import you wish to play. Alternatively, you can obtain the so-called "switchable MultiBIOS" for your Mega/Sega CD. You swap your current CD BIOS with this MultiBIOS and install the appropriate switches, allowing you to play import CD games on your system without the need for an adapter. For more information, check out Arakons guide, available at http://arakon.hn.org/tutorial/bios.html.

Credits

SEGA Enterprises, Ltd.

http://www.sega.com

Manufacturers of my favourite games console of all time, the Mega Drive. Without Sega, this guide would not exist!

Apple Computer, Inc.

http://www.apple.com
Computer manufacturer, developer of Mac OS X. This guide was written on an Apple Powerbook G4 running Mac OS X.
TEXShop http://www.uoregon.edu/koch/texshop A Frontend for the powerful LTEX typesetting system, primarily used for scientic document typesetting.

Eidolons Inn

http://www.eidolons-inn.net
Site devoted to the classic Sega consoles. The Tavern message board in particular was an invaluable source of information during the compilation of this guide.

GoogleTM Groups

http://groups.google.com
A complete archive of every Usenet post since 1981. The alt.sega.genesis newsgroup was used to discuss many aspects of Mega Drive modication.

GameFAQs

http://www.gamefaqs.com
Home of numerous useful Mega Drive documents which were consulted throughout the evolution of this guide. The Genesis message board raised some of the questions included in the FAQ section of this guide.

Special Thanks.

THANKS!
Mike G, Galen Tatsuo Komatsu, Flavio, |Ray| (Arakon), Eidolon, Dark Grue, Samudra, Amano Jacu, Carlo Savorelli, Lorenzo Nocentini and everyone else that has contributed to this guide. I couldnt have done it without you guys thanks!

Disclaimer

This guide has been checked and double checked. To the best of my knowledge, all of the information given here is correct. However, I am not responsible for any damage which results form the [mis]use of this guide. If you have any questions or wish to point out any typos, please contact me via Email. One of the reasons for me writing this guide was because I found it dicult to obtain thorough, reliable information on Mega Drive modications - so I encourage you to distribute this document as much as you want, using any methods you see t (e.g. through websites, le-sharing programs, message boards,. etc.), so that others can have an easier time nding it. Finally, and most importantly, if you feel that you should be credited for any part of this guide, please Email me and you will be added to the "Credits" section in any future releases. Thanks!

Sega Genesis Lightguns

by Eke-Eke (29/07/2008) http://gxdev.wordpress.com/

Introduction

The following document is a compilation of my notes about the Sega Menacer and Konami Justifier lightguns. This mainly covers undocumented aspect of these devices and is principally designed for emulator authors who wants to implement or improve accuracy of lightgun emulation. Please note that NONE of the described features have been tested on real hardware, everything directly comes from analyzing and reverse engineering disassembled gun games ROM images. So, even if it seems to work well on emulators for the mentioned games, some behaviour descriptions or deductions might be incorrect. Feel free to contact me for any correction or comments. Finally, before reading this document, you may want to consult the following publications, which explain important aspects of the Genesis/Megadrive hardware and might be necessary to understand some of the concepts exposed in this document: Sega Genesis hardware notes by Charles MacDonald (gen-hw.txt) Sega Genesis VDP documentation by Charles MacDonald (genvdp.txt) Sega Genesis I/O Chip & Peripherals by Charles MacDonald (gen_io.txt)
The following official documents could also be useful: Official Genesis Software Manual & Technical bulletins from Sega (http://www.spritesmind.net/_GenDev/forum/viewtopic.php?t=227) Sega Menacer patent (US5351969) http://v3.espacenet.com/textdraw?DB=EPODOC&IDX=US5351969&F=0&QPN=U S5351969
I also would like to thanks Tasco Deluxe for providing the Sega Menacer US Patent number. Lightgun games On the Sega Genesis/Megadrive, the following games are known to have gun support: Sega Menacer : o Menacer 6-in-1 game pack o T2: Arcade Game o Body Count Konami Justifier : o Lethal Enforcers o Lethal Enforcers 2
Some Mega-CD games are also known (or rumoured) to have support either for Sega Menacer or Konami Justifier but I haven't actually been able to test them. This document only covers emulation of lightgun games for the Sega Genesis/Megadrive. How lightgun works ? All gun games require the lightgun to be connected on IO port#2 and most of them require a gamepad to be plugged in IO port #1. There is however no known hardware restriction to use them on port #1, it's just that no commercial games actually do this. From software, IO port is accessed through the associated DATA register and configured through the CTRL register. DATA 2 register ($A10005): PD7 PD6 PD5 PD4 PD3 PD2 PD1 PD0 R/W R/W R/W R/W R/W R/W R/W R/W
TH pin TR pin TL pin LEFT pin RIGHT pin UP pin DOWN pin
CTRL2 register ($A1000B): PC7 PC6 PC5 PC4 PC3 PC2 PC1 PC0 HL output control PD6 mode (0:input, 1:output) PD5 mode (0:input, 1:output) PD4 mode (0:input, 1:output) PD3 mode (0:input, 1:output) PD2 mode (0:input, 1:output) PD1 mode (0:input, 1:output) PD0 mode (0:input, 1:output) R/W R/W R/W R/W R/W R/W R/W R/W
(1) guns work by triggering a high to low transition on TH pin (bit6) when their lens sensor detects the pixel beam on TV, so: PD6 (TH) should be configured as an input to be able to detect Gun Position PD5 (TR) & PD4 (TL) are generally configured as outputs and are used for sending commands to the gun. PD3-PD0 are configured as inputs and usually return gun buttons status (2) when bit7 is set, a high to low TH transition will trigger HL input on the VDP side: if bit 3 (IE2) of VDP register #11 is set, a level 2 interrupt is triggered. if bit 1 (M3) of VDP register #0 is set, HVC counter is freezed (latched) for later read.
All Genesis/Megadrive lightgun games enable INT2 triggering and read the HV counter in their interrupt handler. By comparison, on the Sega Master System (or Sega Genesis in SMS compatibility mode), no interrupts could be triggered: games usually have to poll the DATA port and wait for a high-to-low TH transition then read HV counter.
HV counter ($C00008): D15-D8 current vertical line (V counter) D7-D0 current horizontal pixel position (H counter) During active display, V counter corresponds to the current drawn scanline: it starts with $00 and, depending on the height of the active display, ends with $DF (224 lines mode) or $EF (240 lines mode, PAL only). Other values are outside the active display range, which is no concern regarding how gun detection works. According to Charles MacDonald who made tests on a real Sega Genesis, H counter values range is: H32 cell mode (active display = 256 pixels out of 342 pixels) 0x00-0x93 0xE9-0xFF H40 cell mode (active display = 320 pixels out of 422 pixels) 0x00-0xB6 0xE4-0xFF

one H counter unit is equivalent to two pixels. the gap in the counter probably coincides with HSYNC period, when the electron beam returns to the left side of the TV screen. On a side note, it is currently not known if value 0x00 corresponds to the first *active* pixel (pixel 0) or to the first pixel of the left border (blanked). Some games enable HVC latch but some of them does not. In the later case, H counter will obviously return a higher value than the current beam position, due to hardware latency: games will have to take this in account in their gun positioning routine.

Sega Menacer

Technical description This is based on the Sega Menacer patent description. The lightgun is composed of 2 parts: a mobile unit (the gun), detecting raster lines on television thanks to an optoelectronic sensor a fixed unit (IR transceiver/receiver) plugged into the Sega Genesis IO port.
Both units are communicating through IR pulses: 1) the mobile unit is normally constantly transmitting a pulse for each detected scanline. As the gun lens "sees" a circular spot, a variable number of pulses is transmitted. A counter inside the fixed unit detects the received pulses and when the count reaches 8, it triggers the TH signal on the IO port. This is used to average the current Y position of the gun by notifying the game software only once time. 2) When buttons status is required, the fixed unit needs to send an IR sync pulse to the mobile receiver, which responds by a certain amount of pulse (0-15), corresponding to the state of the buttons (4 buttons are mapped). From the Sega Genesis point of view, PD0-PD3 of DATA register will exactly reflect this number of received pulses and the state of each four buttons as well.
The IR sync pulse is controlled by a RST signal, which in fact have two possible lengths:
2 or 3 microseconds: this is the "counter reset" signal, used to reset the above pulse counter. This is sent after receiving button data, at the end of VBLANK. 10 microseconds: this is the "main reset" signal, used to issue the IR sync pulse described above and start buttons data acquisition. This is sent at the beginning of VBLANK.
The RST signal is controlled by software using TH and TR pins (bit5 & bit4 of DATA register)
DATA register PD7 PD6 PD5 PD4 PD3 PD2 PD1 PD0
input output input output input output input output input output input output input output
pixel beam detection (0: visible, 1: not visible) unused unused (unknown value) RST signal level (0: enabled, 1:disabled) unused (unknown value) RST signal length (0: short, counter reset, 1: long, main reset) START button (0: released, 1: pressed) unused C button (0: released, 1: pressed) unused A button (0: released, 1: pressed) unused B button (0: released, 1: pressed) unused

Buttons acquisition sequence To get button status, PD5 & PD4 should be set as outputs and PD3-PD0 as inputs. Then the following sequence is done: 1) "Main" Reset write IO PORT 2 DATA--> 0xff (00000328) 11 write IO PORT 2 DATA--> 0xdf (0000034E) 01 write IO PORT 2 DATA--> 0xff (0000035A) 11 write IO PORT 2 DATA--> 0xdf (00000364) 01 2) read button status read IO PORT 2 DATA 3) "Counter" Reset write IO PORT 2 DATA--> 0xff (0000037A) 11 write IO PORT 2 DATA--> 0xcf (00000384) 00 Y Position As explained above, only one level2 interrupt would happen on each frame, occurring on the line that approximately corresponds to the current gun Y position, preliminary approximation being done by the gun hardware. a) to calculate Y position for the current frame, game softwares usually do some kind of movement interpolation. For example, 6-in-1 game calculates the average V-Counter value from the last eight frames. Body Count and T2: Arcade Game seem to use a more complicated calculation method. (00000372)
b) V counter value is directly converted into an Y coordinate. c) depending on the game or where as gun calibration is possible, a vertical offset is added to the result: Menacer 6-in-1 pack uses 0 by default, T2: Arcade Game uses 8 by default and Body Count uses 16 by default. This is probably done to compensate the fact that the gun does not exactly sees 16 (8x2) lines, depending on the distance between the TV and the gun lens, the visible area is probably larger. d) due to the internal counter inside Menacer hardware, no interrupts could theoretically be triggered on line ($00-$07), making the top eight lines area uncovered by the cursor. X Position a) contrary to V counter value, H counter value is converted into an X coordinate through a precalculated table stored in memory. b) as for Y position, movement interpolation is done by the software as an average of the previous frame's X coordinates. c) an offset is applied by default in the H counter table when converting H counter value into actual X coordinate. 6-in-1 pack uses $4E as offset value and Body Count uses $48, where as T2: Arcade Game uses $84. Notes: this is probably done to take the following hardware latencies in account: o the gun lens "sees" a circular spot so the X centre position is some pixels away from the start of the detection pulse. o there is a delay between detection pulse and TH transition, due to the lightgun hardware latency and IR transmissions. o there is also a delay between TH transition and INT2 triggering or/and HVC latch, due to I/O and VDP chips latencies. o finally, Im not sure if value 0x00 really corresponds to the first pixel of the *active* display area. It might be possible that H counter starts with the first pixel of the left blanked border area. T2:Arcade Game routine does *NOT* set VDP register #0 bit1 (M3) so H counter will NOT be latched. This could explain why the gun routine in T2: Arcade Game uses a larger offset in order to take interrupt level 2 acceptance timing in account. 6-in-1 pack shifts the cursor position for 8 pixels to the left after calculating the interpolated position. This means the last 8 pixels display area cannot be covered by the cursor and that the cursor starts moving eight pixels before the start of the active display area. Depending on the size of the drawn cursor, it will remains invisible or only partially visible. On a similar way, Body Count reduced the active display range, the left and right 8 pixels being inactive.

Here is the H counter range and the corresponding cursor position on screen. All Genesis games use H40 cell mode, other games (such as Sega-CD ones) may use H32 cell mode. Menacer 6-in-1 pack $44-$4D $4E-$51 $52-$B6; $E5-$FF; $00-$0C $0D-$43 T2: Arcade Game $70-$83 $84-$B6; $E5-$FF; $00-$42 $43-$6F BodyCount $35-$47 $48-$B6; $E5-$FF; $00-$34 LEFT BORDER: cursor is fixed ACTIVE DISPLAY: cursor is visible & moving RIGHT BORDER: cursor is fixed LEFT BORDER: cursor is fixed ACTIVE DISPLAY: cursor is visible & moving RIGHT BORDER: cursor is fixed BLANK: cursor is not visible LEFT BORDER: cursor is moving but not fully visible ACTIVE DISPLAY: cursor is visible & moving RIGHT BORDER: cursor is fixed but visible
H counter table values are scaled up, which explains why the cursor "active" range is only 290 pixel counts wide, which is smaller than the 320 pixels active display area. This is probably done to take the fastest pixel clock (used in H40 mode) in account. H counter gap is correctly taken in account but is 2 pixels off (H counter restarts at $E5 instead of $E4). Note that the routine that set the internal H counter table (can be found at offset $315FA in disassembled Menacer ROM) explicitly uses $B6 and $E5 limit values.
From above observations, I found out that a very accurate way to emulate the H counter latch value was to return something like this: hc_latch = hc_table[((gun.x * 290) / 320 / 2) + gun.x_offset) % 211]
with: gun.x_offset = 0x44 (Body Count) , 0x52 (Menacer) or 0x84 (T2: Arcade Game) gun.x being the current cursor position (0-320) hc_table being a table with H counter values as described in introduction. However, if you do not plan to draw your own cursor, perfect positioning is not required and the latency could be accurately emulated instead of using specific game offsets.

Konami Justifier

The "Blue" Gun is connected to the Sega Genesis IO port #2. A "Pink" gun can also be connected to the first gun. A gamepad is required to be plugged into IO port #1. I have actually no informations about how the gun hardware is internally working. DATA register PD7 PD6 PD5 PD4 PD3 PD2 PD1 PD0
pixel beam detection (0: visible, 1: not visible) gun detection (see below, 0: normal, 1: force button state) unused (see below, always return 1) gun selection (0: blue gun, 1: pink gun) unused (see below, always return 1) gun input switch (0: enabled, 1: disabled/reset) unused (see below, always return 0) unused unused (see below, always return 0) unused START button (0:pressed, 1:released) unused Trigger button (0:pressed, 1:released) unused

Gun detection routine Games software execute a commonly used SEGA detection routine, which calculates a 4-bits ID code to determine the type of the connected device. To get the ID code, TH is set to output mode (CTRL2 = $40) and the routine alternately set TH=1 then TH=0. The following logical operation is used to determine each four bits of the ID code: ID3 = (TH == 1) & (DATA bit3 | DATA bit2) ID2 = (TH == 1) & (DATA bit1 | DATA bit0) ID1 = (TH == 0) & (DATA bit3 | DATA bit2) ID0 = (TH == 0) & (DATA bit1 | DATA bit0) a gamepad (6-buttons or 3-buttons) will return ID=0xD Konami Justifier is expected to return ID=0x1
This means the Justifier should return the following byte values when TH is set as output: if TH = 1: DATA = ?1110000 if TH = 0: DATA = ?01100xx with xx different from 00 I'm not sure why Justifier returns such values, maybe setting TH=1 will force input lines to 0.
Notes: bit2 (LEFT pin) & bit3 (RIGHT pin) maybe always return 0 (note that those bits are unused later). even if Justifier is properly detected, the game will once try to read DATA2 register, as if a gamepad was plugged. I don't know if this is an emulation timing issue but if PD5 (TL pin) or PD4 (TR pin) return 0, the game will assume either START or A button as been pressed and will directly jump into the game. Its safer to assumed those bits always return 1 when set as inputs. Button Acquisition To get buttons status, PD5 & PD4 should be set as outputs and PD1-PD0 should be set as inputs. The following sequence is executed at the start of each VBLANK, twice repeated to get buttons status for the two guns: 1) gun acquisition mode is enabled: o bit5 of DATA port is set to select the appropriate gun o bit4 of DATA port is cleared to enable acquisition 2) buttons status is read on DATA port 3) gun is reseted (disabled): o bit5 of DATA port is set to select the appropriate gun o bit4 of DATA port is set to reset/disable acquisition
This has been deducted from analysing the VINT gun routine in Lethal Enforcers: 226(110486): write IO PORT 2 DATA--> 0x00 226(110514): read IO PORT 2 DATA 226(110530): read IO PORT 2 DATA 226(110570): write IO PORT 2 DATA--> 0x10 226(110598): write IO PORT 2 DATA--> 0x20 226(110626): read IO PORT 2 DATA 226(110642): read IO PORT 2 DATA 226(110682): write IO PORT 2 DATA--> 0x30 (00000908) (00000946) (00000946) (0000092A) (00000936) (00000946) (00000946) (00000958)
Gun Position To get gun position, CTRL2 register bit7 should be set to enable HL output triggering and TH should be set as an input. The following sequence is executed at the start of each frame (approx. on line 0), alternately for each gun: 1) gun is reseted (disabled): o bit5 of DATA port is set to select the appropriate gun o bit4 of DATA port is set to reset/disable acquisition 2) gun acquisition mode is enabled: o bit5 of DATA port is set to select the appropriate gun o bit4 of DATA port is cleared to enable acquisition This has been deducted from analysing the VINT gun routine in Lethal Enforcers: (frame N) 0(376): write IO PORT 2 DATA--> 0x10(00000A86) 0(406): write IO PORT 2 DATA--> 0x0 (00000A90) (frame N+1) 0(386): write IO PORT 2 DATA--> 0x30(00000A86) 0(416): write IO PORT 2 DATA--> 0x20(00000A90) Note: Both games give the player the ability to calibrate the guns. Basically, the game will ask you to aim at the centre of the screen then it reads the HV counter and calculates H & V offsets that should afterward be applied on the H and V counters value each time they are read in the level 2 interrupt handler.

X Position Both games use the H32 cell mode (256 pixels active area). By default, the following H counter ranges are used: Lethal Enforcers $00-$7F $80-$FF ACTIVE DISPLAY: cursor is visible & moving INACTIVE
This game does NOT latch HV counter and does NOT use any X offset by default to take hardware latency in consideration. This would mean that, on real hardware, gun calibration is highly advised
Lethal Enforcers II $18-$93; $E4-$E7 $E8-$FF; $00-$17 ACTIVE DISPLAY: cursor is visible & moving INACTIVE
This game does latch HVC but adds a default X offset of $18. Note that the counter gap is correctly taken in account by the software routine.
Y Position No offset is applied by default, the V counter value is directly converted into Y coordinate, active range being $00-$DF.