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The main sign that distinguishes a counterfeit Game Boy Advance SP from an original one
As you know, Nintendo always adds support for games from previous console generations to their consoles, but not as an emulator, but as native support, meaning using original hardware. When you play, for example, on a 3DS, inserting a cartridge from an NDS will activate the second processor, which was added to the console only for backward compatibility.
If we're talking about Game Boy Advance games, a second processor, the Zilog Z80, was added, which was used for Game Boy Color and Game Boy games.
This is a very cool idea, but it requires both certain engineering efforts and financial costs.
How can you tell that the Game Boy Advance in the photo can play old Game Boy Color games? Of course, you can just ask, but we rely on the seller's honest word, which may or may not be enough. Or the seller might be honestly mistaken, having played all their life, thinking they bought an original and selling it as such.
To spot the previously unnoticed "elephant," we had to study mountains of Nintendo patents. Now we'll use this information, gleaned from official Nintendo patents registered with the USPTO (United States Patent and Trademark Office), which describe the practical implementation of combining the ability to play games from different console generations without emulators.
When the Game Boy Advance developers started designing the console, they faced several questions:
1. How to prevent users from inserting new cartridges into old consoles?
2. How to combine support for games from the old console and the new console in one console (since the Game Boy Color had the same processor, despite the color screen, and didn't require adding a new one)?
3. How to show the console that an old cartridge is inserted, not a new one (this is especially relevant, considering that they are supplied with different voltages).
And so on.
And Nintendo engineers came up with an interesting solution.
Interesting fact: through the software part of the console, you can't tell which cartridge is connected. That is, in the program, you can't write a line like "if the cartridge is old, then do this."
What happens when a cartridge is inserted into the console?
First, let's understand what happens when a cartridge is inserted into the console? To do this, let's look at the Nintendo patent diagram, where Nintendo described the operation of this system:
So, after we insert the cartridge (into the cartridge slot, labeled 37 on the diagram), we turn on the console (with switch 382, which is the console's on/off switch).
Switch 35, based on the state of selector 35s, determines which cartridge is inserted and, using chip 384, sets a value of 1 or 0 in register 362f (1 for new games and 0 for old ones).
Regardless of the value set in register 362f, the processor reboots and activates the 32-bit core (362a), after which the instructions set in the second boot ROM (362e) start running. At a certain point in these instructions, the value set in the register (362f) is checked, and if it's set to 1, the 32-bit processor continues its work, but if it's set to 0, chip 369 is activated, which stops the processor (362a) and activates the 8-bit processor (361a) with its own instructions (361c).
What is clear from this diagram and procedure? That the parts responsible for determining which cartridge is inserted are labeled on the diagram with numbers: 37, 35, 35s, and 383.
Parts 37, 35, 35s, and 383
To understand what these are, it's not enough to just look at the board, because without understanding what they are and what they do, it's unclear what to pay attention to.
Let's try to figure it out. We know that from the software side of the console, there's no way to tell which cartridge is inserted, so this is implemented externally and happens when we insert the cartridge into the console. If you look closely at the cartridges, you'll see that new Game Boy Advance cartridges have a notch on the back, labeled 412 in the picture. And on old cartridges (GB or GBC), there is no such notch.
To understand how this notch affects things, let's look at another Nintendo patent, which describes the operation of a special device designed to work with different types of cartridges.
Top view:
And what happens when different types of cartridges are inserted:
As you can see, with the same size cartridge slot, it's the notches in the new cartridge that prevent the lever from switching selector 35s, while in the old cartridge, these notches are absent, and they, on the contrary, affect selector 35s.
Let's see how this switch looks on real hardware - the Game Boy Advance.
This lever (35s) is marked in red:
So, by inserting this cartridge, we simply push this selector all the way and close other contacts. This way, switch 35 understands that an old cartridge is inserted and sets the register value to 1.
We've finished figuring out how the process of determining which cartridge is inserted works. And surely you have a question, how can this help us identify a counterfeit, and especially a Game Boy Advance SP, not just a Game Boy Advance?
Main Sign of an Original
As you understand, the Game Boy Advance SP is made using the same technology as the regular Game Boy Advance, and it also has the same selector, here it is:
It does exactly the same thing, only it's positioned slightly differently. It is not part of the cartridge slot itself, but a completely independent and separate part. And for some time, this part was made at the same Foxconn factory that now produces iPhones (top view of the board):
And if you look closely, you can see that very lever:
It's clear that pirates couldn't replicate such a complex circuit, especially one made in well-organized factories. And all this resulted in the fact that if you look inside a counterfeit, you'll see emptiness, without any switches!
