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IREM M72 / M92 converts

The M72 (R-Type…) and M92 (R-Type Leo, In The Hunt…) are IREM platforms with motherboard + game ROM board. Their lock is not a suicide battery, but a protection MCU (i8751) present on most games. Since the MCUs have been dumped (MAME), conversions are possible with the right MCU (or its substitute).

IREM M72 (1987)

Field Value
CPU NEC V30 @ 8 MHz
Sound CPU Z80 @ 3.58 MHz
Sound YM2151 (+ DAC samples)
Media ROM daughterboards (the game) plugged into the motherboard
Protection i8751 MCU (on most games)
  • Games: R-Type, R-Type II, X Multiply, Dragon Breed, Ninja Spirit, Image Fight, Legend of Hero Tonma, Hammerin' Harry…
  • ROM board: the game sits on plug-in ROM boards; R-Type takes two ROM boards. Variable sizes (e.g. R-Type $40000 ROM).

The i8751 protection MCU

"Most games have an i8751 protection MCU." It shares RAM with the main program (region $b0000-$b0fff), does a RAM-inversion test at boot, and provides a routine that the main program jumps into (instead of a simple return).

→ Without the right i8751 (or its dumped contents), the protected games crash. The MCUs have been extracted and archived (MAME emulates them) → a base for conversions and de-protected versions (the protection code is neutralised).

Confirmed M72 games with i8751 MCU (MAME, config m72_8751)

Battle Chopper / Mr. HELI no Daibouken, Ninja Spirit / Saigo no Nindou, Image Fight, Legend of Hero Tonma. (The bootlegs of these games exist with a generic i8751 — hence "bootleg with i8751" sets in MAME.) Other M72 games use PAL protection rather than an MCU — check the irem/m72.cpp driver per game.

IREM M92 (1991)

Field Value
CPU NEC V33 @ 9 MHz
Sound CPU NEC V30 @ 7.16 MHz
Sound YM2151 + GA20 (IREM custom PCM)
Video Nanao GA21 & GA22 customs
Media motherboard + game ROM board
Protection i8751 MCU (per game)
  • Games: R-Type Leo, In The Hunt, Gunforce (1/2), Undercover Cops, Ninja Baseball Bat Man, Blade Master, Major Title 2, Hook, Superior Soldiers…
  • Same logic: common motherboard + game ROM board + optional i8751.

Converting an M72 / M92 (summary)

  1. Gather the target game's ROMs (V30/V33 program, graphics, sound).
  2. Burn the EPROMs and fit the ROM board (in the right positions).
  3. Handle the MCU:

  4. protected game → supply the game's i8751 (or a version whose protection is patched/neutralised, like the de-protected "bootleg" sets),

  5. unprotected game → nothing special.

  6. Test: sprites (Nanao GA21/22 on M92), sound (YM2151 + GA20), MCU-driven gameplay.

The MCUs are dumped

IREM preservation's big win is the dumping of the i8751: it makes emulation faithful and enables conversions/de-protections on real hardware (MCU substitute, or patched code).

Program EPROM, game by game

Size → EPROM: 64 KB → 27C512 · 128 KB → 27C010 · 256 KB → 27C020. The program is on a daughterboard. M72: many games have an i8751 MCU (shares RAM $b0000-$b0fff, dumped by MAME → replaceable). M92: generally unprotected (Nanao GA customs, no MCU). (Source: MAME irem/m72.cpp, irem/m92.cpp. Board view: IREM M-series PCB.)

M72

Game Program EPROM MCU
R-Type 4× 27C512 — (unprotected)
Battle Chopper / Mr. Heli 6× 27C512 i8751
Ninja Spirit 8× 27C512 i8751
Image Fight 2× 27C512 + 2× 27C010 i8751
Legend of Hero Tonma 4× 27C010 i8751
X Multiply 2× 27C010 + 2× 27C512 —
Dragon Breed 2× 27C512 —
Air Duel 4× 27C010 —
R-Type II 4× 27C010 —
Gallop / Cosmic Cop 2× 27C020 —

M92

Game Program EPROM
Gun Force 4× 27C010
Blade Master / Cross Blades 2× 27C020 + 2× 27C512
R-Type Leo 2× 27C020 + 2× 27C010
Hook 2× 27C020 + 2× 27C010
Mystic Riders 2× 27C020 + 2× 27C512
Undercover Cops 2× 27C020 + 2× 27C010
Lethal Thunder 4× 27C010
Ninja Baseball Bat Man 4× 27C020
Superior Soldiers 2× 27C020 + 2× 27C010
Perfect Soldiers 4× 27C020

Settings (DIP)

M72 and M92 are configured with physical DIP switches — two banks of 8 (DSW1 / DSW2):

Bank Typical functions
DSW1 coinage, test/service, flip screen, sound in demo
DSW2 difficulty, lives, bonus/extend, coin mode

After a conversion, apply the target game's DIP table (see general convention).

Before / after

  • Game without MCU: reprogram ROMs → another game, simple.
  • i8751 game: conversion possible with the right MCU (or a de-protected version); without it, a crash.

Where to read more

Sources & attribution

Review & corrections

How this space is used

Spotted a wrong value, an outdated procedure, a chip reference that does not match your board? Say so here, with what you observed (model, board revision, serial number, measurement). Every report is cross-checked against a source before anything changes — an unverifiable correction is published as “reported by …, not cross-checked” rather than silently applied.

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