Datel first developed their Action Replay cartridges for the Commodore 64 in 1986 1. The Action Replay line then went on to include products for the NES, Super Nitendo, Nintendo 64, Playstation and various handheld consoles.
Since Datel have produced many chat cartidges and other custom unlicensed console hardware we have split this section into its own page:
Romantic Robot released their Multiface One for the ZX Spectrum in 1986 2 which allowed Memory Dumps similar to save states in modern emulators, cheats could then be applied to these memory dumps with the POKE command.
Vintage Sinclair Archive provides a comprehensive directory of technical resources for the Multiface series (I, 128, and +3). The archive includes essential reverse engineering data such as ROM dumps, hardware schematics, and original user manuals for these legendary NMI-based hardware debuggers and snapshot devices used on the ZX Spectrum.
Lost Retro Tapes has a detailed write-up about reverse engineering and re-creating the Romantic Robot Multiface 128 for the Sinclair Spectrum.
The author outlines the painstaking process of photographing the original PCB, tracing all component connections and vias with a multimeter to generate a complete KiCad schematic, and then designing a modern, compact PCB layout for fabrication. This recreation provides a fully functional version of the classic game-hacking tool.
The Game Genie was one of the first Cheat Code cartridges to be developed for home consoles as they realised their first version for the Nintendo Entertainment System (NES) in 1990.
Gaming Historian presents a detailed history of the Game Genie, a popular cheat device originally developed by Codemasters. The video covers the legal battles between Nintendo and Galoob (the US distributor) over copyright infringement and derivative works, eventually establishing important precedents for fair use in gaming.
It also briefly explains the technical method of operation: the device intercepts and modifies data signals between the game cartridge and the console (e.g., preventing the “lives” counter from decrementing) to enable cheats like infinite lives.
Nintendo feared that this would either cause harm to their brand or make game piracy even easier and thus decided to sue Galoob Toys and Camerica. Both companies eventually won the court case after four long years and got a nice bonus out of it: $140 million! This cash injection more than covered their court fees and allowed Codemasters to expand and develop more games 3.
Justia hosts the full text of the landmark 1991 U.S. District Court decision that validated the legality of the Game Genie.
The court ruled that the device, which temporarily modifies game data to enable cheats (like infinite lives), does not create an infringing “derivative work” because the changes are not permanent. Furthermore, it established that a consumer’s private use of the device to alter their own purchased games constitutes fair use, setting a vital precedent for reverse engineering and aftermarket software tools.
In an interview with GSHI (a now defunct website) Richard Aplin who worked on the Game Genie line of products as a hardware engineer had the following to say 4:
We had no way to get any info on the hardware or software of the consoles (and we had a very litigious relationship w/Nintendo) , so we did it “the hard way” by reverse-engineering them - by literally going to a store, buying a few systems, tearing them apart, and attaching a logic analyser to them.
A logic analyser is basically like a digital oscilloscope (shows you what high-speed signals are doing in real time) but typically has lots of separate channels (32-48). You connect each channel to signals/chip pins that look “interesting” inside your console, run the analyzer, then spend some time figuring out what all the signals are doing and what the hell is going on.
Once you’ve got the basic signals figured out (typically you want to figure out the pinout of the cartridge connector) - found the address and data bus of the CPU and the basic control lines (Read, Write, etc) then you’ve got to the point where you can typically build a ‘dev board’.
He then goes on to explain the contents of the dev board:
We’d build a PCB (with suitable cartridge edge connector on it) that contained an EPROM, an FPGA, a bunch of SRAM, a high-speed parallel port, and typically for fun a 2-line LCD display and some lights. The eprom contained whatever boot code was required to get the console booted, then it entered a monitor program where you could remotely view/change the console memory using the parallel port on the board. The parallel port always used the ubiquitous “PDS” style interface (PDS= Programmers Development System, at the time a very widely used - and very fast - PC-based cross-assembling system by Andrew Glaister and others) so everything was fairly standard.
In the same interview Richard Aplin explains that they created custom hardware and software running on a Commodore 644:
We usually used a custom PCB that had (typically) a parallel port, a passthru connector for the original cart, and basic byte-replacement hardware. Also a few simple tools running (I think) on a Commodore 64.
This software was presumably very similar to how Cheat Engine works, take a dump of memory, loose a life in the game, then take another dump and compare the memory addresses that have changed.
For the ROM level cheats it would be harder, presumably they would take a full ROM dump and run it through a disassembler as best they could, then see what the program counter’s value is at when it writes to the memory address you are interested in and find that in the disassembly.
Also I love this quote from the same interview, it shows just how time consuming it would be to support a whole book of codes for the NES library 4:
They had teams of people making codes (a guy called Graham Rigby was the main Codemeister - he lived in a room full of nothing but shelves and racks of NES games - he had every NES game in every territory I think)
Presumably they has similar rooms with Game Boy, Game Gear and Sega Mega Drive games stacked high, I wonder what happened to all those games!
Datel Action Replay Professional V-Ram functionality You could press a “Freeze button” on the Action Replay to “see images not normally visible during playing of the game”. The video seems... ...
