Skip to content

Reflex Prism

Lag-free, resolution-preserving HDMI-to-analog conversion for RGB, YPbPr, and S-Video displays.

Buy Reflex Prism Latest firmware

Prism is not a scaler

Prism does not upscale or downscale. A 15 kHz CRT needs a 240p, 480i, or 576i HDMI source mode. Use a separate downscaler if the source can output only 480p, 720p, or 1080p and the destination is a 15 kHz display.

Composite video is unsupported

Composite is electrically present on the Mini-DIN-10 output, but visible dot crawl is expected. Use RGB, YPbPr, or S-Video for supported operation.

What Reflex Prism does

Reflex Prism converts compatible RGB-formatted HDMI video to analog video without scaling, cropping, or changing the aspect ratio. The analog output timing and resolution match the HDMI input.

  • One-to-one conversion

    Lag-free digital-to-analog conversion with the source resolution, crop, and aspect ratio preserved.

  • Flexible analog output

    HD15 provides RGB or YPbPr; Mini-DIN-10 provides RGB and S-Video simultaneously at 15 kHz timings.

  • Independent stereo audio

    Buffered stereo audio is available from both the 3.5 mm jack and Mini-DIN-10 connector.

  • Upgradeable and configurable

    Current firmware exposes EDID, sync, and video-path controls through the local PRISM browser dashboard.

Connections and output limits

Output Connector Formats Limits
HD15 video HD15 female RGBHV, RGBS, YPbPr Up to 1920x1200 when the source and display support it; output resolution matches the HDMI input.
Multi-format AV Mini-DIN-10 female RGBS, S-Video Intended for 240p, 480i, and 576i-class 15 kHz input timings.
Stereo audio 3.5 mm TRS and Mini-DIN-10 Buffered analog stereo Both outputs can be used independently.

Quick setup

MiSTer to a 15 kHz CRT

Use this when: Using RGB, YPbPr, or S-Video with a consumer CRT, PVM, or other 15 kHz display.

  1. Connect MiSTer HDMI to Prism HDMI input.
  2. Connect the appropriate HD15 or Mini-DIN-10 cable to the display.
  3. Select RGB or YPbPr for the HD15 output as required by the display and cable.
  4. Apply the MiSTer.ini settings below, then restart the active core.
  5. Confirm the display supports the timing before changing modes.
  6. Use direct_video=1 as a compatibility fallback if direct_video=2 is not supported by the installed MiSTer main build.
  7. Earlier pass-through units may require composite_sync=1; current units with internal sync handling use composite_sync=0.

Recommended settings:

direct_video=2
vga_mode=rgb
composite_sync=0

HDMI source to a PC CRT or VGA display

Use this when: The source can produce a resolution and refresh rate accepted by the connected high-resolution analog display.

  1. Connect the HDMI source to Prism and the HD15 output to the display.
  2. Select RGB for a VGA or PC CRT input.
  3. Configure the source for a timing supported by the display.
  4. Use the display EDID through Prism when possible, or choose a known-safe source mode manually.
  5. For MiSTer scaler output, leave video_mode unset to prefer the display EDID or set a known-supported mode manually.

Recommended settings:

direct_video=0
vga_mode=rgb
composite_sync=0

Configure Reflex Prism

The current Prism firmware provides a local dashboard from the USB PRISM drive.

  1. Connect Prism USB to a desktop computer.
  2. Open the PRISM drive and launch PRISM.HTM. Older firmware may label the dashboard INDEX.HTM.
  3. Open the file in desktop Chrome or Edge and press Connect.
  4. Select Reflex Prism from the serial-device picker.
  5. Review live status before changing EDID, sync, or S-Video settings.
  6. Save intentional changes; saved configuration and the Custom EDID slot persist across power cycles.

Notes:

  • Safari and iOS Safari do not support the live Web Serial connection.
  • A valid connected VGA display EDID has first priority in the normal EDID route, followed by the Custom EDID slot and the selected built-in fallback.
  • Keep a known-good display mode available when experimenting with EDIDs.

Update firmware

Use the single current prism_dac firmware release for supported RP2040-equipped Prism hardware.

  1. Download the latest prism_dac UF2 from the official releases page.
  2. Open PRISM.HTM from the PRISM drive in desktop Chrome or Edge and connect to the device.
  3. Choose Update Firmware. Prism will restart as an RPI-RP2 drive.
  4. Copy the prism_dac UF2 to RPI-RP2.
  5. Wait for Prism to restart, then reopen the PRISM dashboard and verify the saved configuration.

Notes:

  • Firmware updates preserve the saved Custom EDID slot; clearing or factory-resetting it is a separate action.
  • Do not use experimental or diagnostic firmware unless support specifically requests it.

Troubleshooting

The 15 kHz CRT does not lock or shows no picture.

  • Confirm the HDMI source is actually outputting 240p, 480i, or 576i-class timing.
  • Confirm vga_mode=rgb and the correct direct_video setting.
  • Check whether the display and cable require RGBS, YPbPr, or S-Video.
  • Confirm the HD15 RGB/YPbPr selection matches the cable and display.

A PC CRT has no picture or unstable sync.

  • Use RGB with separate sync and composite_sync=0.
  • Choose a source resolution and refresh rate supported by the display.
  • Prefer the connected VGA display EDID when it is available.

The dashboard cannot connect.

  • Use desktop Chrome or Edge.
  • Close other serial terminals or browser tabs using Prism.
  • Reconnect USB, reopen PRISM.HTM from the PRISM drive, and select Reflex Prism.

Composite video has dot crawl.

  • Composite output is unsupported and dot crawl is expected.
  • Use S-Video, RGB, or YPbPr instead.

Frequently asked questions

Can Prism connect a modern console to a 240p CRT?

Not by itself. Prism preserves the HDMI input resolution. Modern consoles can be used with compatible PC CRTs, but a separate downscaler is required when the destination accepts only 15 kHz video and the source cannot generate a 15 kHz HDMI mode.

Does Prism add lag?

Prism performs one-to-one digital-to-analog conversion without a scaling frame buffer.

Can HD15 and Mini-DIN-10 be used at the same time?

Yes. The outputs are simultaneous, subject to each connector's supported formats and timing limits.

Which firmware file should I use?

Use the current unified prism_dac UF2 from the official Reflex Prism releases page.

Cables and accessories

Sources

Open this guide on another device

QR code for the Reflex Prism guide

Open the current online guide

Public-safe product source: public-docs/data/products/.