I developed a board that can be installed inside a NES or Famicom to improve the video quality. This is not a replacement PPU (Picture Processing Unit, the NES graphics chip) nor does require any parts from Nintendo arcade hardware. The original idea came from HardWareMan and thefox on the NesDev forum.
The NESRGB board effectively bypasses parts of the PPU - Palette RAM
(Color Generator), Decoder, and DAC. These functions are duplicated in
the NESRGB board with a focus on video quality. The timing of the video
is unchanged so there is no lag (no framebuffer, no VGA, no HDMI, etc,
etc), just non-interlaced 15kHz video output.
I have uploaded some high res screen shot photos here:
Drakon has created video captures from the board (Youtube links).
Gimmick, Castlevania 3, Kirby's Adventure
Full Castlevania 3 Playthrough
How it works (technical)
Refer to the operation block diagram. The PPU part of the diagram is taken from US patent number 4824106.
An Altera PLD sits between the PPU and the CPU data bus. When the CPU writes data into the Palette Ram (Color Generator) the data is captured and stored in the NESRGB board. Modified data is passed to the PPU. The PLD also intercepts writes to the register controlling the operation of the Multiplexer, making EXT0-3 outputs. The modified data passed to the PPU removes data already available at the EXT0-3 outputs. The rest of the information required (EXT4, blanking, and sync) is extracted from the video output with comparators. The video data is then decoded from the palette currently selected and passed out to the DAC and video encoder.
The NESRGB board is designed with the NES front loader in mind. It sits in a socket where the PPU normally lives. The PPU is mounted in the NESRGB board. See the picture below as an example (ignore the jumble of wires soldered to the card edge finger at the bottom of the NES motherboard, it is not related to the installation). It also shows a separate voltage regulator board which is recommended for the original NES because the its own voltage regulator heat sink is small and may get too hot with the additional load from the NESRGB board.
The board may also be installed into AV Famicom and top loading NES models when a suitable pin adapter board is fitted.
Switch wiring info - A three position toggle switch is now included instead of a slide switch.
Where to buy
Buy from etim online shop (Australia, International),
For questions and comments please email.
10/2/2019 - Added the link to the Software and Errata page.
27/9/2015 - Updated pinout and jumper diagram for V1.4 hardware.
9/12/2014 - New install guide for the original Famicom.
30/8/2014 - Added a install guide for the Famicom Twin
15/2/2014 - Added a install guide for the Famicom AV
30/12/2013 - Removed Paypal buttons, added link to new shop.
13/11/2013 - Added installation guide for the original Famicom.
22/10/2013 - NESRGB boards are temporarily sold out.
20/10/2013 - created.