89 votes
Accepted

How exactly does Sonic & Knuckles' 'Lock-On Technology' work?

How does the Sonic & Knuckles cart detect another cartridge? It checks the serial numbers of games; they can be found in the ROM's header. It probably detects all preceding Sonic the Hedgehog ...
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39 votes
Accepted

How did people program for Consoles with multiple CPUs?

It varies machine to machine; at the simplest end is the Neo Geo — its 68000 and Z80 have completely independent buses. You write one program for the 68000 and one for the Z80 and a single pipe of ...
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  • 32.4k
37 votes
Accepted

How did the Sega CD decompress video?

We used to have to write our own video playback system, so each game did it differently. I worked on Microcosm for the SegaCD and if I recall we used a 16 colour palette for the video playback and had ...
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29 votes

Why was the Sega Genesis marketed as a 16-bit console?

... the Motorola 68000, was a 32-bit processor. As already written in Raffzahn's answer, Motorola itself said that it is a 16-bit processor. And as far as I know, the reason is not the external 16-...
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28 votes
Accepted

Amiga 500 OCS/ECS vs Mega Drive VDP

The [pre-AGA] Amiga: uses a planar frame buffer, stored in memory that is shared with the CPU (and which therefore reduces the CPU's speed); provides dual-playfield hardware scrolling, but the total ...
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17 votes

How did the Sega CD decompress video?

Playback of compressed digital video is handled entirely in software on the Sega CD which is why FMV games on it play with the video taking less than the full screen and at relatively low frames per ...
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  • 4,032
14 votes
Accepted

Why was the Sega Genesis marketed as a 16-bit console?

the Motorola 68000, was a 32-bit processor. I'd say 16 Bit - likewise Motorola did (*1). The bitness of a processor is and always will be up for discussion, as various features may not operate at the ...
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  • 168k
13 votes
Accepted

If the Sega Genesis/MegaDrive could be overclocked so easily, why couldn't the SNES?

The Super NES (SNES) has a much different hardware architecture than the Sega Genesis, and is built around the custom Ricoh 5A22 ASIC. As opposed to the discrete, stock, Motorola 68000 CPU employed in ...
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12 votes

What is going on in the overscan area of Sega Genesis games?

Short answer: No. At least not for display purposes. The pixels shown are artefacts when the VDP is operation in modes with more than 224 lines (NTSC). These lines were usually not displayed on real ...
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  • 168k
12 votes

How does Master System backwards compatibility work on the Megadrive?

The 68000 does nothing; it is entirely disabled. Ditto the Yamaha OPN. The Mega Drive's VDP is almost entirely backwards compatible with that of the Master System — it implements the graphics mode ...
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10 votes

How did people program for Consoles with multiple CPUs?

There are two basic techniques: shared memory and dedicated communication ports. Shared memory simply allows both processors to access the same memory bus. There are some issues, as the bus has to be ...
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  • 13.7k
10 votes

Amiga 500 OCS/ECS vs Mega Drive VDP

The Megadrive comes from an arcade machine lineage, it's cut-down Sega arcade machine hardware. The Amiga comes from a computer lineage, it's an evolution of the Atari 800, same designer, and many of ...
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  • 380
10 votes

What is going on in the overscan area of Sega Genesis games?

The color RAM in the Genesis video chip is single ported such that at any given time the color RAM data bus either contains the data being read out of it for display purposes, or the data being ...
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9 votes

Why was the Sega Genesis marketed as a 16-bit console?

It's usually the width of the system data bus that determines the "bitted-ness" used to describe the system. While the Motorola 68k CPU used as a component in the Sega system certainly has some ...
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  • 56.8k
9 votes
Accepted

Graphics Editor for 16-Bit Games

Depending on the platform we're talking about, you've got a few choices. As the best platform for editing images at the time was the Amiga with its 4096 color palette in HAM mode on OCS/ECS (Original ...
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  • 1,017
8 votes
Accepted

What ended the Sony console partnerships with Sega and Nintendo?

There was a relationship between Sony and Nintendo starting in 1988 and into the early 1990s as someone in Sony was looking to get into the video game business after seeing how successful the Famicom ...
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8 votes
Accepted

What cleaning/repair can be done to a Mega Drive cartridge slot?

Have you tried cleaning the pin connector inside the Mega Drive? It's fairly simple to remove the shell and access the pin connectors. (don't forget to remove the LED wires for model 1) I got a second ...
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  • 919
7 votes
Accepted

Sega Genesis and Sega CD interaction

To answer the first half of your questions: The right-side 60-pin expansion slot is bespoke, and found on Mega Drive / Genesis 1 and 2 only. It is not present on the Genesis 3 or Nomad. It exposes the ...
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  • 9,875
6 votes

Self-modifying code in commercial games for the (S)NES, Gameboy, Genesis/MD, PC Engine, Atari, etc

I rarely had occasion to use self-modifying code. Doing that had a lot of overhead both in ROM space and RAM space, and I rarelysaw an occasion where it would be worth it. I did do it on the IBM PC, ...
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6 votes

Self-modifying code in commercial games for the (S)NES, Gameboy, Genesis/MD, PC Engine, Atari, etc

RAM and ROM are reachable by the CPU for execution, so most consoles can execute code from RAM. The consoles using cartridges usually don't have a lot of RAM, so I think it's VERY rare if someone ...
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6 votes
Accepted

Self-modifying code in commercial games for the (S)NES, Gameboy, Genesis/MD, PC Engine, Atari, etc

I know about one Atari 8bit game called Robbo. There are source codes published where in file R1.ASM you can see: LDA LMVT,X STA JMP1+1 LDA LMVT+4,X STA JMP1+2 JMP1 JMP * LMVT ...
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  • 257
6 votes

Sega Genesis/Mega Drive ROM Disassembler

DGEN emulator has a starscream 68k core with a builtin dissasembler and debugger . ` might be the key to break into it once rom is running. It's also easy to recompile with SDL as the gfx/audio ...
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5 votes

If the Sega Genesis/MegaDrive could be overclocked so easily, why couldn't the SNES?

It's an issue of integration. On the early Genesis systems the custom chips and CPU were physically separate from each other so it was easy to isolate the various clock signals and replace the CPU ...
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5 votes

Amiga 500 OCS/ECS vs Mega Drive VDP

TL;DR: For all of this it might be helpful and take a step back from bits and bytes and take a step back to look at the whole process of Game development. Doing so will show that quality is much more ...
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  • 168k
5 votes

Building a Sega Genesis Classic Portable - What kind of display?

In the video you linked (at 01:12), I notice that this device has the standard yellow and white connectors for composite video and audio. Many cheap portable LCD TVs support this kind of input, and ...
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  • 7,644
5 votes

"Genesis Lock-On Technology" to change the language of a Famicom game

I'll assume you only want to modify small parts of the game, rather than the entire game. (If you wanted to modify the entire game, you'd just make a new cartridge holding the entire image.) Your ...
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  • 246
4 votes

Amiga 500 OCS/ECS vs Mega Drive VDP

Let's assume your assumption "MegaDrive games are generally 'better' than Amiga games" was true - Which is a statement hard to prove and very probaby only backed by opinion: Games Console vs. Home ...
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3 votes

Self-modifying code in commercial games for the (S)NES, Gameboy, Genesis/MD, PC Engine, Atari, etc

The NES game Gimmick! uses self modifying code as part of its anti-piracy check failure response. 96 bytes are decrypted while being copied from ROM to RAM and then jumped to. This is to hide a ...
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  • 159
3 votes

How did graphics processing for old 8/16bit consoles work & what are the differences between an FPU/maths co processor & a graphics card?

The video circuitry was a lot simpler in those days and there was no true GPU as we have today. The video memory was part of the CPU memory space and any video circuitry merely converted it into a ...
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