Saturday, October 28, 2023

The Unofficial Enhanced NESs - Continuing On where Nintendo Left Off

As we all know, Nintendo introduced the Famicom in 1983, ported it to the west as the Nintendo Entertainment System in 1985 and after the last licensed games were released in 1993-94 Nintendo retired the system. But that does not mean that the hardware underlying the system was dead, the hardware was widely cloned and cartridges were still being made for it. Some companies decided develop the hardware further by adding new capabilities, such as new graphics modes and more sound channels, to work with games that would look less primitive than those that could only take advantage of 1983-era chip designs. Let's take a look at some of these approaches in this blog article.

Nintendo itself has pushed the NES design to new capabilities with the SNES, which was originally supposed to be backwards compatible with the NES but that capability was dropped when it would have added significantly to the console's cost. Hudson Soft had a great deal of experience with developing Famicom games and partnered with NEC to make the PC Engine, which was also very heavily influenced by the Famicom's hardware.

Other companies unofficially took up the charge by making enhanced console hardware that was backwards compatible with original NES games.  One of the first companies to make an enhanced clone chip was UMC, which had plenty of experience in making clone chips of the NES's CPU and PPU. Their enhanced clone chip, the UM6578, is able to display 16 colors per tile instead of the 4 colors that a standard NES can show. 

Space Castle - UM6578

The company known as V.R. Technology later developed a line of NES clone chips with increasingly enhanced capabilities, the VT series. The main chips are the VT02, VT03, VT09, VT32 and VT369 and unlike UMC's offering, they were backwards compatible with standard NES games. V.R. Technology also made even more advanced chips, such as the VT1682, alongside these 8-bit chips which had SNES like features but were not compatible with NES or SNES games. 

The VT series of chips use a unified memory bus called the OneBus. An original NES has a separate CPU and PPU and each have their own address and data busses to access memory. A typical NES cartridge will have a PRG-ROM chip connected to the CPU bus and a CHR-ROM or CHR-RAM chip connected to the PPU bus. Most products using VT and UM6578 chips were Plug 'n Play devices containing only a single ROM chip. A ROM chip inside a VT02 or better PnP would have all its data and graphics stored in one chip which, if the game were developed as an ordinary NES cartridge would come on two chips. The OneBus interleaves memory accesses between the VT02's CPU and PPU to the single ROM chip. 

Konami Collector's Series꞉ Arcade Advanced - VT03

OneBus and UM6578 60-pin cartridges are rare but they do exist and will not work in a regular Famicoms. Consoles with VT chips can be backwards compatible with regular NES and Famicom cartridges by using the pins to detect whether to use the OneBus or the split bus mode. UM6578 consoles begin in backwards compatibility mode and use a pair of register writes to enter the enhanced but not backwards compatible UM6578 mode.

The VT02 started by offering relatively modest improvements such as duplicating APU channels, adding a 2048 tile mode, improved graphics DMA and dedicated DMA functions for full 8-bit PCM audio output but these features were seldom used. VT02 games usually looked and sounded like regular NES games as much of this functionality had been previously implemented in different ways in mapper chips like the MMC5.

Virtual Ping Pong - VT03

The VT03 made the first obvious improvements and is the most common chip which actually shows graphics which an NES cannot. The VT03 has improved graphics DMA, dedicated DMA functions for full 8-bit PCM audio output, support for 16x16 sprites, a 4096 color palette and 64 color sprite and background tiles. The VT09 was a cost-reduced version of the VT03 which used 16-bit graphics fetches in order to use slower memory chips but this required rearranging the graphics storage in a way that is incompatible with the VT03. The VT series chips have reversed duty cycle rectangle wave audio channels like many unenhanced NES clone NTSC CPUs, so when they are running games made for original NES and Famicom systems, they frequently do not sound correct. 

From the VT09 the evolution of the VT series split into two incompatible directions. The VT32 added a hardware multiplier and divider and adding independent two channel ADPCM/PCM playback but at the cost of removing the second APU channels. The VT369 was far more impressive, offering a 3x faster CPU mode, a separate ADPCM sound unit with its own CPU and 256-color sprites and tiles with 15-bit RGB color palette support. The VT389 added high resolution 512x480 interlaced graphics support, Games developed with the earlier chips tend to look and sometimes sound something like a NES game, but VT369 & VT389 games usually look and sound far more advanced even if their gameplay has all the hallmarks of 8-bit design.

dreamGEAR My Arcade Gamer V - VT32

These chips found their way into many, many plug and play devices which were sold in stores like Walgreens, Target and Wal-mart. The Plug and Play devices can come in many varieties, handheld consoles with built-in screens, joysticks or gamepads that connect to a TV, mini-arcades, sealed boxes that use some other console's look and have controller ports. The Oregon Trail Electronic Handheld used a VT369 with an external sound chip, the Konami Collector's Series: Arcade Advanced joystick used a VT03 and the "8Bit Games Mini Game Box" uses a VT02. The Lexibook Compact Cyber Arcade licensed Disney, Pixar, Star Wars and Marvel properties and use the VT369. 

There was a console that accepted UM6578 cartridges, the Timetop. The Timetop can use a motion controller that functions like a Wiimote, although its sensing technology is probably nowhere near as advanced. The Powerjoy Supermax used a VT02 and had its own OneBus cartridges. The Yobo Factor 5 uses a VT03 and came with a OneBus multicart with original games. The Generation NEX used a VT03 but I do not know if anyone ever tested a VT0x cartridge in its Famicom slot. The NEX was widely criticized for its reversed rectangle wave duty cycles and incompatibility with MMC5 games like Castlevania III, so the VT0x chip's backwards compatibility was not perfect. While there are no known consoles exist that accept cartridges that support functionality beyond the VT03, there are a few handhelds which come with an SD card to load games and have some advanced VT support.

Lexibook Compact Cyber Arcade - Marvel Ultimate Spider-Man - VT369
Images rotated for the handheld screen that the game used

The games for these systems were developed by Chinese companies such as Nice Code, Jungletac, Cube Tech and Waixing even if the hardware was released by other companies like Lexibook, which is a French company. Jungletac's developed games for the UM6578 first and later ported games over to the VT03, but the original UM6578 versions are better versions of those games despite using less capable hardware. Nice Code's games tend to be rough around the edges but show a decent degree of professionalism in the graphic design. 

Some devices contain entirely "original" games, but many devices of the multicart variety include pirated NES and Famicom games and repeats to pad out the number of advertised games. Like many standalone multicarts for the basic Famicom or NES, these games may be obscured by name changes, graphic tile hacks and music which plays altered notes. Even "original" games may take music or sound effects from an NES or Famicom or take 4 color tiles and redraw them as 64 color tiles.

If you want to play "Enhanced NES" games, you can try to track down these various PnPs and consoles, but there are some emulators which support them. MAME has some support, but if you want full support, NintendulatorNRS is the only choice. Several NES 2.0 mappers have been assigned to these Enhanced NES chips: 256, 296, 405, 407, 408, 419, 423, 424, 425, 426, 427, 436. Many VT02 games could work or be playable on a standard NES running a flash cart but the games requiring a more advanced NES clone will not run on standard NES hardware. Theoretically if a flash cart like the EverDrive N8 Pro can completely reassign the hardware signals of its cartridge pins, it could run VT03 games when inserted into a VT03 console. The ROMs in these Plug and Plays can reach 16, 32, 64 and even 128 MiB in PRG-ROM size and the N8 Pro supports a maximum of 8 MiB PRG-ROM + 8 MiB CHR-ROM, so it would not be able to play all of them even if the PPU capabilities were on the VT level. 

Lexibook Retro TV Game Console - Frozen - 300 Games - VT389
Left Image has a native 512x480 resolution, Right Image is upscaled 256x240

An article like this can only scratch the surface of this subject, there are hundreds of plug and play devices which use enhanced NES clone chips, even if the games that run on them do not always take advantage of their special features. Dumping the ROM content from these systems requires special hardware skills as the silicon dies of these chips are often bonded directly to the PCB and covered in epoxy, a.k.a. "glop tops". Many devices have been dumped but there are an unknown number out there which have not. More information about games, companies and devices which used Enhanced NES chips can be found on the Bootleg Games Wiki.

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