When connecting a laptop/dock to a monitor, the right direction matters. Many “converter” cables only work one way. If the cable's intended direction doesn't match your source (video output) and display (video input), you'll get no signal. Even if the connectors fit.
Key terms
Lets start by defining some terms so that we are all on the same page.
- Source (Output): Laptop, dock, GPU port sending video
- Display (Input): Monitor/TV/projector receiving video
- Uni-directional: Works only one way (e.g., DP to HDMI)
- Bi-directional: Works both ways (common with HDMI to/from DVI, DP to/from mDP)
- Active adapter/cable: Has electronics to convert formats/directions (e.g., DisplayPort to HDMI)
- Passive adapter/cable: No electronics; relies on the source to convert video signals (e.g., Dual-Mode DisplayPort/DP++ to HDMI)
What typically works and what doesn't
| Scenario | Directionality | Requirement | Notes |
|---|---|---|---|
| DisplayPort (DP) source to HDMI display | Often uni-directional (DP to HDMI) | Passive may work with DP++; otherwise use an active DP to HDMI | Many docks/GPUs support DP++, but some do not so please check specification |
| HDMI source to DisplayPort display | Uni-directional (HDMI to DP) | Active HDMI to DP adapter | A DP to HDMI cable won't work in reverse |
| USB-C (DP Alt Mode) source to HDMI/DP display | Uni-directional | Alt-Mode USB-C to video cable/adapter | Not reversible (you can't feed HDMI into USB-C) |
| Thunderbolt source to DP or HDMI displays | Uni-directional | Thunderbolt/USB-C video adapter | Behaves like USB-C Alt Mode for displays |
| HDMI to/from DVI | Bi-directional (passive) up to 1080P | Simple adapter/cable | Same TMDS signaling |
| DP to/from Mini-DP | Bi-directional (passive) | Simple cable | Same protocol |
| Digital to/from VGA (analog) | Direction varies | Active converter | Digital/analog conversion required |
Rule of thumb: For DP to/from HDMI, assume DP to HDMI unless the product explicitly says HDMI to DP (Active).
Docking stations: quick notes
- USB-C & Thunderbolt docks: DisplayPort or HDMI native outputs are available on many models, DP++ is not supported.
- DisplayLink controlled DisplayPort outputs generally support DP++ and passive adapters.
- DP MST daisy-chaining requires DisplayPort MST compatible displays connected via DisplayPort cables - DisplayPort to HDMI adapters are not recommended.
Resolution, refresh, and features
- Available resolution/refresh (e.g., 4K60) depends on source + cable/adapter + display
- Features like HDR, HDCP, and VRR may require specific active adapters and sufficient bandwidth
- For long cable runs, signal redrivers may be required. Active adapters may have reduced cable length, for example DisplayPort sources provide about 50 percent of the power of a HDMI source. DisplayPort signals are more efficient than HDMI and require less power for the same cable length. When converting to HDMI the overall cable length will be less than a native HDMI source.
Shopping checklist (esp. on Amazon)
- Check the pictures: Listings often show Source to Display with icons/arrows (match this to your setup)
- Read the title/bullets: Look for explicit direction (“DP to HDMI,” “HDMI to DP (Active)”)
- Scan specs: “Active” vs. “Passive,” DP++, supported resolutions, and any power needs
Quick examples
- Dock (DP out) to Monitor (HDMI in): DP to HDMI cable/adapter; use active if DP++ isn't supported or for higher reliability
- Laptop (HDMI out) to Monitor (DP in): Active HDMI to DP adapter required
- USB-C laptop (Alt Mode) to HDMI monitor: USB-C to HDMI cable/adapter; not reversible
FAQs
Why doesn't my "DP to HDMI" cable work from an HDMI laptop to a DP monitor?
Mot likely it is a uni-directional (DP to HDMI) cable. Most adapter cables (DisplayPort Plug to HDMI Plug) are passive uni-directional cables, while most adapters (DisplayPort Plug to HDMI Socket) are uni-directional active or passive adapters.
My desktop video cards has one HDMI and three DisplayPort outputs. To enable four HDMI displays do I need passive or active adatpers?
Most graphics cards can support a native HDMI and single Passive DisplayPort to HDMI display, in the graphics card itself there are normally two DisplayPort to HDMI adapter chipset, one dedicatd to the HDMI port, the second available for a single passive adpater. For enabling four HDMI displays we recommend either three active, or two active and one passive adapters/adapter cables.
Why aren't most DisplayPort (source) adapters bi-directional?
DisplayPort data is transmitted in discrete data packets, this makes DisplayPort the most flexible video standard (for example tunneling in Thunderbolt, or converting to other display types). However converting from a non-packet based video stream to packets requires more comptational power, many early HDMI to DisplayPort (uni-directional) adapters required a separate 5V power source - often USB. While some modern adapters can utilize the HDMI or DisplayPort source power, these often have limited (6ft/2m) cable lengths.
If you have any questions please feel free to contact us at support@plugable.com and we'll be happy to help!
