I needed a way to test the output stream of mod chips that didn't require attaching a logic analyzer. Thus was born the Mod Chip Reader Chip. The MCRC would listen on a pin like the CD controller of a PSX for boot strings. When it found a boot string, it would 1) blink one of 3 LEDs to ell me what string it found, 2) output the string in ASCII form on another pin that could be attached to a computer's serial port so as to observe the data, and 3) it would display the timing of the 'leading' and 'trailing' edges of bit transitions incoming on the bitstream sensing pin. This chip was really cool. it was programmed into a Zilog Z86E04 and had a PC board made for it compelte with switches, LEDs, serial interface to a PC, power supply so that it did not need a PSX to run it, and a 'ZIF' socket for dropping in an 8 or 18-pin mod chip to study. The MCRC was useful for lots of things, but the single-most useful part it played was the front end for my grand idea: the "Anti-Piracy" Mod Chip.
After letting the source code out for the basic mod chip, I got to thinking, "well, this will piss off game store owners, so let's work on something for them. I'll take the code for my MCRC for rewrite it to do something nifty. It will read the wobble groove data in real-time as it comes from the CD drive and at the right moment, gate off the wobble data and inject a magic character to boot the game." Thus was born the *ultimate* mod chip in early February 1997. Using the same four wires as a classic 8-pin mod chip (two for power, 1 gate, 1 data), the chip would start up listening to the wobble data logic pin on the output side of the converter opamp. Eventually, a data block would show up if the disc being booted had such a wobble groove encoded. This means that only original game discs would boot, and copies or 'silvers' would fail. The originals could be from any of the three territories: U/C (United States/Canada), JPN (Japan), or EUR (Europe/Australia). These three territories had their respective 4-character boot strings, the first three characters of which were the same: 'SCE'. The last character was the real magic: 'A' for Americas, 'E' for Europe, 'I' for International (Japan, using the root name for SCEI: S*ny Computer Entertainment International). The 'SCE' characters were parsed by the Anti-Piracy (AP) Mod Chip program, and if it found all three, a special event happened: the AP chip would assert its gate signal, cutting off the 4th character coming from the wobble groove. Knowing the timing of the 3 characters just received, the AP chip would then transmit the 4th character itself. The PSX was satisfied it had a valid game disc, and the game booted up.
This code I sold for $50 to anyone interested. I made a killing. The AP chip could not and to this day cannot be detected by anti-modchip game code. It has no way to know it is there as the chip only acts when an actual wobble-boot block is being observed from the CD drive. Thus, the AP chip became the first (and best as it was foolproof) Stealth Chip. Oh yeah, I coined the term 'Stealth Chip', too, at least as in regards to mod chip lore.