So when I was a kid I was told by my friends that SNES games that had the extra card edge pieces on the left and right meant that the game had the "FX Chip" which meant that the game was super mega awesome cool. I still believed this up until today. I got a Game Genie in the mail and noticed it didn't have the extra receptacles to accept the "FX Chip" games. But after a few hours of playing Castlevania 4 i thought i would give it a try and plug in "Doom" into the game genie and see what would happen. After all, Doom's Box boasted that the game was equipped with "FX". So i threw it in and the weirdest thing happened, IT WORKED! So i opened up the cart to see if those extra "FX Chip" contacts even went anywhere. From what I gather, Only ONE of the 16 contacts are even connected to anything, and it appears to come to a dead end. I was blown away by this. I'm not saying that the game doesn't include some extra mechanism, but it obviously has no correlation to the additional card edge contacts like i have always though. So I looked though all my SNES carts and the only other game that I own that has the additional contacts was "Kirby Super Star" which never claimed to have any special "FX" chip or anything as far as i can remember. This time, there are 2 out of the 16 connected and they actually go somewhere. also, this game wont work with the game genie. well, anyway. i had a small bit of my understanding of video games blown out head today. does anyone know what the extra contacts were for if not the fx chip?
a) I have no idea how many layers a SNES cartridge PCB is but it's possible that there are internal traces going somewhere from the extra pins. b) From the image there it seems that Kirby Super Star uses an SA-1 chip, which you can find out more about here. EDIT: http://www.caitsith2.net/snes/flashcart/cart-chip-pinouts.html is an interesting read, seems that the pins aren't addon chip specific. EDIT2: My guess is that the addon chips are using the 21.477MHz clock somehow, and the regulations stipulated that if one side of extra pins was needed then the other would also have to be included.
I know star fox won't display anything without the extra pins. But you can hear the music and game react to buttons commands. I am guessing that doom uses the fx chip more for processing then displaying any graphics. Now that I think about it did nintendo always have those extra pins on the cart slot for any possible expansion chips when they created the snes or was this just a design oversight that worked in their favor?
Star Fox I believe uses the Clock Signal on the SNES Cartridge port which is on one of the outter pins that most carts don't have. Without it the Super FX chip won't work. All other Super FX games have their own clock crystal. Super Gameboy 1 uses the signal on the port where as Super Gameboy 2 has its own crystal. Super FX is a RISC processor clearly aimed at software rendering 3D graphics and other fucntions needed for a 3D game. It was used in a couple handfuls of games. Most are 3d like Star Fox, Stunt Race FX, Dirt Trax FX, and so on. One notable 2D game taking advantage of it is Super Mario World 2: Yoshi's Island. It's used for scaling and other effects as I've heard. So it's great for processing particularly things related to graphics. Besides the clock signal there are other signals on the extra edge connectors. I don't recall what they are. Kirby Superstar and Dreamland 3 use the SA-1 chip which is way different than the Super FX. It boasts its own 65816 processor (the same kind as the SNES has already) but it's clocked at a faster speed. SA-1 also has a slew of other enhancements. Unfortunately from what I've heard from byuu (the author of the BSNES emulator) the SA-1 was never fully utilized by any games. So much more possibly could have been done with it. It was not aimed at 3D games though. Mega Man X2 and X3 use Capcom's Cx4 chip for some processing as well. You may notice while X1 has noticeable slowdowns, X2&3 do not have much. Part of this may be the way the Cx4 helps process sprite characters taking load off the CPU. I'm pretty sure these games have the extra connectors too.
If you pull out an old SNES emulator you'll quickly see where the SFX chip is used. When you start a level and its a black background with text the effects to transition to the gameplay is done by the SFX chip IIRC. Super sized sprites and a few other items as well. Though of note Yoshi's Island plays just fine when plugged into a Game Genie. The extra pins don't get connected at all with one.
It scared the living fuck out of me when I saw it move, as I'm half-awake as I type this. Far more awake than I was a few minutes ago, for certain.
Wasn't Batman and Robin coded by a group that used to be demo scene coders? I am sure they are using all kinds of nice tricks.
Awesome! I noticed the same thing when I was a kid. Star Fox didn't work with the Game Genie (since it doesn't pass those extra side contacts) and yet to my surprise Doom did work. I knew that Doom uses the SuperFX2 chip witch is clocked faster than the original SuperFX chip in Star Fox. But now I know why it works.
The extra pins are primarily for decoding stuff with an auxiliary address bus, expansion audio (Super Game Boy) and supplying the 21 MHz master clock. Some games with coprocessors supply their own oscillator, others will use the master clock.
