Question about game and watch emulation

[alank2]

I loved those LCD games when I was a kid.  Many of the game and watch series like Donkey Kong, etc., but my favorite is Bandai Zaxxon LCD.  It had two LCD screens layered in a sandwich one on top of the the other.  Over the years I've seen emulators for some of these devices - my question is how is someone emulating these?  Were they actually running a microcontroller?  I assumed it was some sort of custom logic chip.

[T3sl4co1l]

Presumably, the same as any other console: a microprocessor with ROM, where the MP is constant and the ROM varies.  I suppose one would need photographs of the LCD segments as well, making the emulation file unusual compared to other consoles (where the only additional data required might be a BIOS ROM and save files).

Tim

[SeanB]

Those old games used a very simple microcontroller, generally an Intel 8048, 8051 or other version of the Intel 8 bit  microcontroller family, that is both cheap and has around 2k of mask ROM in it.  Then the game also had a small LCD interface chip ( or on later ones a simple gate array with both parts on one die) to drive the display, generally a Hitachi LCD driver chip. That was enough space to fit a simple game in, and was cheap and easy to implement.

Emulators simply use a more powerful microcontroller and a graphical LCD display, and use the original ROM image ( or a clone of the actual game) in a virtual machine, or a rewrite to the later instruction set, and a set of graphical images to emulate the on screen estate on the graphical LCD display.

[orolo]

I owned and loved some of these games when I was a kid. There are teardowns in youtube, and internally they all look alike: a board with protruding RTC crystal, one electrolytic, maybe an LED and some passives. In the center, a rectangular hole for a CPU, marked according to the game (PP-22 seems to be Popeye:
,
 OC-22 is Octopus
 ,
watch both videos at the 1:00 minute mark.) The chip is marked Nintendo, probably custom built?

These games must be easy to emulate: they are glorified LED flashers, a simple state machine that takes a few inputs and turns on different LCD sections based on its state, emitting a beep here and there. The more complex part is probably the clock. The only doubt emulating these, I think, is what RNG they used, if any. Most of the CPU pins must be digital outputs to directly control the LCD. I don't know about the state of ROM tech in the early 80's: maybe these simple I/O intensive chips are all the same, programmed with a different one-shot ROM at the factory, and then marked. Or maybe they are slight variations of the same chip at the silicon level. I don't think they bothered to solder a separate ROM chip somewhere.

----

Oh, well, after writing this I saw SeanB's answer. So the ROM tech is mask ROM, and the chip some generic 8-bit Intel clone. I was just speculating based on the teardowns.

[SeanB]

There were some teardowns where the actual processor in the chip was a 6502, as that is simple enough to put into a cheap low cost ASIC, and the ROM was also implemented in the final mask metal layer as well, allowing the manufacturer to make many different games with the same basic die, only the final step in manufacture ( etching that final layer) determining the actual chip that would come out, allowing flexible manufacture as demand changed or a new game came out.

The major thing was to get the size of the die as small as possible and as cheap as possible, to keep the cost down. 100 different game types, all using almost the same case moulds, printed circuit board ( keeping the cost down as well, no need to change any assembly jig or test setup) and only the display itself, or the overlay on the top, the silkscreen on the case and the manual being different between games. I saw a lot of them with the same basic case style, but only those differences.

[rjardina]

Most if not ALL of these are simulators and not emulators.

The biggest differences between emulators and simulators are; Emulators act like the hardware and
use a rom (the game) to run on top of it. A simulators is coded from the ground up including the game
and hardware. Unless the coder is intimate with the game, most of them will not act or play correctly
I've never hear of anyone dumping the rom on a game and watch or something of the like. I would
love to be corrected on someone dumping the LCD game data. It would be cool to see if it could be done.

[T3sl4co1l]

Most if not ALL of these are simulators and not emulators.

The biggest differences between emulators and simulators are; Emulators act like the hardware and
use a rom (the game) to run on top of it. A simulators is coded from the ground up including the game
and hardware. Unless the coder is intimate with the game, most of them will not act or play correctly
I've never hear of anyone dumping the rom on a game and watch or something of the like. I would
love to be corrected on someone dumping the LCD game data. It would be cool to see if it could be done.

Yeah, that's the reason why it feels doubtful that true emulation would be used.  Dumping a mask ROM that doesn't need an external bus, is very different from dumping a cartridge that literally provides a bus right there for you!

While it's possible, it's about as much effort as (or maybe more than?) reconstructing a simulation of it.  But gosh, a simulation isn't going to be very accurate if the creator has never tested edge cases in the original article.  Even just the timing from button press to display change could be wrong, let alone how and when the buttons are scanned and processed (though at least that can be measured externally -- again, at quite some effort).

I've never heard of an emu/simulator for those handhelds, but I'm no expert on such things.

Tim

[rjardina]

I've never heard of an emu/simulator for those handhelds, but I'm no expert on such things.

Tim

They are out there. Google play has a few, and others have made them for PC and other platforms.
Nintendo even make a few Game Boy games called "Game & Watch Gallery" where they have between
5 to 20ish on a cart (I do not know if this is emulated or simulated). Both in the classic LCD simulator
and a modern updated version. I am personally not aware of the game that was asked in topic though.

[Bicurico]

Read this: http://emulation.gametechwiki.com/index.php/Game_%26_Watch

MAME can emulate a few. The problem is dumping the ROM and identifying the CPU.

All the other "emulators" are really just simulators.

Still, it is fun to visit this site: http://pica-pic.com/zelda/
(Requires Flash - use Internet Explorer)

Cheers,
Vitor