The 10NES is a CIC (Checking Integrated Circuit) lock-out system designed for the North American and European versions of the Nintendo Entertainment System, which had three main purposes:
- To give Nintendo complete control over the software released for the platform
- To prevent unlicensed (pirate) game cartridges from running
- To prevent games importing (regional lockout)
Various companies found ways to bypass the authorization chip.
The system consisted of two parts, a microchip in the NES that would check the cartridge in the system for authentication, and a microchip in the cartridge that would give the 10NES code upon demand. If the cartridge did not provide the authentication, then the 10NES would reset the CPU during every cycle until a game with the authorization chip was inserted. The constant resetting of the CPU would stop the NES from booting up. However in some instances, the 10NES has been prone to reset the CPU if it fails to authenticate a licensed cartridge. The 10NES was patented under U.S. Patent 4,799,635 and the source code was copyrighted; only Nintendo could produce the authorization chips. The patent covering the 10NES expired on January 24, 2006, although the copyright is still in effect.
The 10NES chip was only installed in the model NES-001 Control Deck, not the model NES-101.
NES consoles sold in different regions had different lockout chips, so games marketed in one region would not work on consoles from another region. Known regions are: USA/Canada (3193 lockout chip), most of Europe (3195), Asia (3196) and UK, Italy and Australia (3197). Since two types of lockout chip were used in Europe, European NES game boxes often had an "A" or "B" letter on the front, indicating whether the game is compatible with UK/Italian/Australian consoles (A), or the rest of Europe (B). Rest-of-Europe games typically had text on the box stating "This game is not compatible with the Mattel or NES versions of the Nintendo Entertainment System". Similarly, UK/Italy/Australia games stated "This game is only compatible with the Mattel or NES versions of the Nintendo Entertainment System".
Because the 10NES in the model NES-001 Control Deck occasionally fails to authenticate legal cartridges, tinkerers at home discovered that disassembling the NES and cutting the fourth pin of the lockout chip would change the chip’s mode of operation from "lock" to "key", removing all effects and greatly improving the console’s ability to play legal games, as well as bootlegs and converted imports.
- Most unlicensed companies created circuits that used a voltage spike to knock the authentication unit in the NES offline.
- A few unlicensed games released in Europe and Australia (such as HES games) came in the form of a dongle that would be connected to a licensed cartridge, in order to use that cartridge's 10NES lockout chip for authentication.
- Tengen (an Atari Games subsidiary) took a different tactic: the corporation obtained a description of the code in the lockout chip from the United States Patent and Trademark Office by claiming that it was required to defend against present infringement claims in a legal case. Tengen then used these documents to design their Rabbit chip, which duplicated the function of the 10NES.
Legal proceedings on Tengen:
- A small company called RetroZone, the first company to publish games on the NES in over a decade, uses a multi-region lockout chip for NTSC, PAL A, and PAL B called the Ciclone which was created by reverse engineering Tengen's "Rabbit" chip. It is the only lockout chip in existence that will allow games to be played in more than one region. It is intended to make the games playable on the original NES-001 hardware that uses the 10NES lockout chip and the two other regions - the other region free alternative would be the top-loading NES, which does not feature the lockout chip. The Ciclone chip is the first lockout chip to be developed after the patent for the 10NES had expired.