Intel D8751H

XianXi

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I have an Irem board that has one of these. According to the datasheet it's an EPROM that doubles as RAM?

The board placement of this chip says PR, I'm guessing it's the program rom but in mame there is no dump of this chip.

Game is Legend of Hero Tonma.

The game on boot sometimes says RAM is bad and it isn't, everything in between has been tested and verified good and this is the last thing left to check.
 
The D8751H is an MCU (microcontroller) with UV-erasable EPROM for the program memory. It seems to be used mainly as a protection device on this game.

Here's what the MAME driver C code has to say:

Protection simulation

Most of the games running on this board have an 8751 protection mcu.
It is not known how it works in detail, however it's pretty clear that it
shares RAM at b0000-b0fff.
On startup, the game writes a pattern to the whole RAM, then reads it back
expecting it to be INVERTED. If it isn't, it reports a RAM error.
If the RAM passes the test, the program increments every byte up to b0ffb,
then calls a subroutine at b0000, which has to be provided by the mcu.
It seems that this routine is not supposed to RET, but instead it should
jump directly to the game entry point. The routine should also write some
bytes here and there in RAM (different in every game); those bytes are
checked at various points during the game, causing a crash if they aren't
right.
Note that the program keeps incrementing b0ffe while the game is running,
maybe this is done to keep the 8751 alive. We don't bother with that.

Finally, to do the ROM test the program asks the mcu to provide the correct
values. This is done only in service, so doesn't seem to be much of a
protection. Here we have provided the correct crcs for the available dumps,
of course there is no guarantee that they are actually good.

All the protection routines below are entirely made up. They get the games
running, but they have not been derived from the real 8751 code.

It's not clear to me if the 8751 is actually involved in the RAM check. The maws updates page says the this device was decapped, de-protected and read, but I've no idea where to find the dump.
 
The D8751H is an MCU (microcontroller) with UV-erasable EPROM for the program memory. It seems to be used mainly as a protection device on this game.

Here's what the MAME driver C code has to say:



It's not clear to me if the 8751 is actually involved in the RAM check. The maws updates page says the this device was decapped, de-protected and read, but I've no idea where to find the dump.

Sounds to me like each game has a slightly different program, so you'd need a dump from that specific game. There may not be a dump for Legend of Hero Tonma... You could write your own 8751 program based on the MAME code and it would work, even though it wouldn't be "authentic".
 
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