Modchips

The modchips used on the PlayStation 1 (PS1) are a variety of devices designed to bypass the console’s built-in media authentication system. It's important to clarify that this mechanism isn't exactly "copy protection" in the conventional sense. Instead of checking the content of the disc itself, the PS1's security system is focused on identifying whether the media has a unique "fingerprint" that matches a licensed disc. Essentially, the system performs a check to determine if the disc is an official, authorized product. This is why methods like the "swap trick" were so effective — as long as a legitimate, licensed game disc was present when the console performed its initial media check, it could later be swapped for a backup or copy, and the console would continue to boot the new disc without issue.

The reason for this is that the console wasn't verifying the data written on the disc but instead looking for specific characteristics tied to the official discs produced by Sony. Once the licensed disc was detected during the boot process, the PS1 would allow the swap to occur. However, later revisions of the PS1 introduced more advanced boot ROMs, which included an additional media verification step, making the process more complex. As a result, these updated consoles required a "double swap" — the player would need to perform two disc swaps to bypass both checks, further complicating the procedure.

This incremental change in the PS1's security reflects the console manufacturer's attempt to counteract these workarounds, but modchips, along with swap tricks, remained effective tools for circumventing these measures throughout the lifespan of the console.

Modchips

1. Old Crow

In 1997 a new modchip was released called “Old Crow”. This new modchip was another clone of the original modchip, but the source code was released to the public, reducing the cost of the chip even further. “Old Crow” was originally made for the Zilog Z8 microcontroller, but versions were released for the PIC16C54, and PIC16C84 as well.

Later in 1997 the “Old Crow” code was ported to the then new PIC12C508 microcontroller, which is still being used for modchips today. The new chip dropped the modchip prices to the price range they are still sold at today.

Mayumi V4

This was particularly notable as the first chip to deliver excellent stealth capabilities for the PU-22 and later machines. As the "V4" in the name suggests, Mayumi had developed several other chips before this one, all of which were well-designed. However, the V4 stood out for incorporating a groundbreaking feature: it used the XLAT signal to disable SCEx injection.

• Compatible with PU18 and later boards.
• Two timing options are available for PU18/PU20.
• Incompatible with PU7/PU8, as it relies on the mechacon clock, which differs on these boards.
• By using the mechacon clock, the timing is highly consistent across chips, ensuring reliable performance.

MM3

This appears to be a modified and patched version of the Mayumi V4 code. The key changes include switching to an internal clock (enabling compatibility with PU7/PU8 boards), simplified mode switching, and partial stealth support for PU7/PU8 systems.

• Supports PU7/PU8 boards, though stealth functionality is not fully optimized.
• 4-wire non-stealth mode is supported.
• Requires one fewer wire (mechacon clock) compared to the original Mayumi design.

PSNee

This is a later chip - it was designed to run on Atmel based Arduinos, although it can also run on standalone ATTINY chips. It uses a unique stealth method that decodes the SUBQ data from the CD drive and controls the SCEx injection based on that, and may be the only chip that provides 100% stealth on the PU7 and PU8 boards.

• New universal stealth method for improved compatibility and performance.
• Requires only 6 wires on most boards.
• Supports boot ROM patching for PAL PSone consoles.
• Floats all I/O pins when not injecting data, significantly reducing or eliminating the PM41(2) pickup noise issue.

OneChip

This modchip is specifically designed for the PAL PSone and shares similarities with the Mayumi V4 and MM3 in terms of code. However, certain features, such as mode selection, have been removed (as the PSone lacks a reset button). Notably, it includes a boot ROM patch to bypass the PAL PSone's territory check.

Stealth Chip 2.8a

A modchip designed for the Sony PlayStation 1 (PS1), enabling the console to bypass regional lockouts and play backup or imported games. It is particularly compatible with early PS1 models, such as the SCPH-100x series, which feature PU-7 and PU-8 motherboard revisions.