Prism delivers clean RGB, YPbPr, and S-Video from compatible HDMI sources, with flexible audio over Mini-DIN 10 and 3.5mm. For RGB and S-Video, your HDMI source must support 240p, 480i, or other 15 kHz output modes. Custom EDID support, ADAC compatibility, and upgradeable firmware make Prism ready for the setup you have now and the features coming next.

Features

Lag free 1:1 digital video to RGB, YPbPr, and S-Video conversion
No resolution upscale/downscale
No crop/aspect ratio changes from input to output
Reference quality simultaneous video output
- HD15 (VGA) port:
  - RGB or YPbPr (controlled by physical switch)
  - Up to 1920x1200 (matches digital video resolution - see resolution chart below)
  - Use this to convert 240p-1200p digital video to analog video for a high resolution monitor, PC CRT, etc.
- Mini-Din 10 (Sega Saturn AV) Port:
  - RGB and S-video simultaneously
  - Composite video is present, but not supported due to dot crawl
  - 240p/480i only (~240p/15kHz HDMI special resolution required)
    - Supported by MiSTer’s Direct Video and Raspberry Pi special mode lines, but not modern PCs or consoles
HiFi audio output
- Buffered stereo audio for independent 3.5mm and Mini-Din 10 audio output.

Web Configurator (V1.1 and newer)
- Plug in Prism to a PC and open the "Prism" drive
- Open INDEX.HTM in Chrome or Firefox (not Safari)
- Press Connect
- Select "Reflex Prism (COMXX)"
- Dynamic EDID (V1.1 and newer)
  - 4 internal EDIDs that are prioritized in the following order
    - VGA monitor EDID passthrough
    - User customizable EDID
    - Custom Prism EDID or ”ADAC” EDID for third-party FPGA consoles
- Software Sync Selection (Web Configurator)
  - Composite sync or separate sync to HD15 (VGA) and RGB on Mini-Din 10
  - Composite sync is required for S-video on Mini-Din 10
- Dynamic S-Video output
  - Auto - disables output if separate sync is detected (experimental)
  - On - Enables port
  - Off - Disables port

Includes

Reflex Prism Unit

MiSTer Configuration

MiSTer FPGA MiSTer.ini 240p/480i configuration:
- direct_video=2 (Use “1” as a fallback until MiSTer main updates)
- vga_mode=rgb
  - Prism requires RGB video as the input format. It converts from RGB to YPbPr, and S-Video.
- composite_sync=0 (Prisms shipped after March 2026)
- composite_sync=1 (Prisms shipped before March 2026)
MiSTer FPGA MiSTer.ini 480p+ configuration:
- direct_video=0 (“2” for auto direct video mode)
- vga_mode=rgb
- composite_sync=0 for PC CRTs that don’t support composite sync.
- video_mode=_ (“1” for 1024x768, “6” for 640x480, etc.)
- ;video_mode=_ (use monitor’s EDID preferred resolution)

Officially Supported Resolutions (not including custom resolutions)

Firmware

Latest firmware available here.

Instructions:

Plug into a PC
Open the "WebHID.htm" in Google Chrome or Firefox
Press the "Connect" button
Select "Reflex Prism" from the list and press "OK"
Once connected, press "Update Firmware" button in the top right of the web browser
The device should reboot as a usb storage device called "RPI-RP2"
Copy .uf2 file to the RPI-RP2 drive
Device will apply firmware, and reboot back into Reflex Prism mode.

Tested Devices

Geometry or aspect ratio adjustments may be required. No guarantee of compatibility with all of these devices as firmware is always subject to change.

Consumer CRTs and PVMs
- MiSTer FPGA (RGB/YPbPr and RGB + S-Video)
- Groovy MiSTer
PC CRT / HDTV VGA
- MiSTer FPGA (Analog IO board to consumer CRTs + Prism to PC CRT)
- PC to PC CRT
- SteamDeck to PC CRT
- Mac mini to PC CRT
- GCVideo to RGB (note: regenerate csync in GCVideo might not work for YPbPr)
- Wii2HDMI to PC CRT
- Wii U to PC CRT
- Switch to PC CRT
- Switch 2 to PC CRT
- PS3 to PC CRT
- PS5 to PC CRT
- Xbox Series X to PC CRT
- Dreamcast HDMI to PC CRT

Peripherals

HD15 (VGA) to YPbPr cable
HD15 (VGA) to SCART cable
Mini-Din 10 to SCART cable
Mini-Din 10 to RCA + S-Video cable (Universal)
Mini-Din 10 to HD15 (VGA) cable for Extron and some video upscalers (RGBS and audio only)
Slim Profile 3.5mm to RCA Audio Cable (Amazon Affiliate)

Changelog

V1.0

Initial Release

V1.05 - Shipped February/March 2026

Added internal H+V to Composite sync circuit
- Internal switch toggles between sync pass or combine for HD15 port
  - Set to pass by default

V1.1 - Shipped April 2026

- Web configurator
  - Dynamic EDID
  - Software Sync Selection
  - Dynamic S-Video output
  - Future firmware features possible

Troubleshooting

What video formats does Prism support?

Prism expects RGB formatted HDMI video and outputs the same resolution as input. Prisms delivered in 2026 include a composite sync combination circuit.
HD15 (VGA): RGBHV or YPbPr (use slide switch to select)
Mini-DIN-10: RGBs and S-Video

Can I connect Switch/PS5/Steam Deck to my 240p/15kHz CRT?

No, that requires a downscaler. HDMI minimum resolution is 480p. You can use Prism to connect those consoles to a PC CRT.

Why do I see dot crawl in my composite video signal?

Composite video is not officially supported. It is affected by dot crawl. There's no technical solution to improve the composite video signal.

How do I enable audio and video output on my A****gue FPGA Console?

Make sure your firmware is up to date to support the DAC. Enable High Impedance Headphones in the settings to get audio working.

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