What Is DisplayPort Dual-Mode (DP++)?

DisplayPort Dual-Mode, commercially designated as DP++, is an optional feature built into many DisplayPort video sources that enables them to transmit HDMI and DVI video signals directly through a DisplayPort connector. By allowing the graphics processor to switch transmission modes automatically, DP++ enables users to connect their modern computers to HDMI or DVI monitors using inexpensive, passive cable adapters instead of costly active converters.

How DisplayPort Dual-Mode Works

Standard DisplayPort transmits video and audio data in micro-packets, similar to how Ethernet or USB operates. In contrast, HDMI and DVI use a continuous signaling method known as Transition-Minimized Differential Signaling (TMDS).

Because these two transmission methods are fundamentally incompatible, a standard DisplayPort output cannot communicate with an HDMI display without a signal conversion chip. A DP++ enabled port solves this at the hardware level:

  1. Detection: When a passive adapter is plugged in, the source device detects an electrical pin pulled to a specific voltage (via the DisplayPort configuration lines).
  2. Mode Switch: The graphics card recognizes that an HDMI or DVI display is attached and reconfigures its internal transmitter to output TMDS signals natively instead of native DisplayPort packets.
  3. Signal Adjustment: The passive adapter merely acts as a level shifter to adjust the DisplayPort’s 3.3V signaling to the 5V signaling required by HDMI/DVI, without needing to process or reconstruct the video stream.

How to Identify a DP++ Port

Source devices with Dual-Mode support are typically marked with the standard DisplayPort logo accompanied by two plus signs (DP++). If an output only features the standard DisplayPort logo without the plus signs, it likely only outputs standard DisplayPort signals, meaning it requires an active adapter to connect to HDMI or DVI displays.

Passive Adapters vs. Active Adapters

Understanding the difference between adapters is essential when using DP++:

  • Passive Adapters: These adapters do not contain signal-conversion processors; they rely entirely on the source port having DP++ capability. They are affordable, compact, and ideal for standard single-display setups connecting a DP++ PC to an HDMI or DVI screen.
  • Active Adapters: These adapters contain an onboard conversion chip that receives standard DisplayPort packet data and actively re-encodes it into an HDMI or DVI signal. Active adapters are required if the video source does not support DP++, when using multi-monitor setups (such as certain multi-display docking stations or older AMD Eyefinity setups) that exceed the GPU's native TMDS clock generators, or when driving high-bandwidth displays beyond the passive specification.

Limitations of DisplayPort Dual-Mode

While DP++ simplifies display compatibility, it has bandwidth constraints based on its version:

  • Type 1 DP++: Limited to a maximum TMDS clock rate of 165 MHz. This allows resolutions up to 1080p (1920x1080) at 60 Hz or single-link DVI resolutions.
  • Type 2 DP++: Increases the TMDS clock limit to 300 MHz, aligning with HDMI 1.4 specifications. This enables 1080p at 120 Hz or 4K resolution at 30 Hz.

Dual-Mode does not natively support HDMI 2.0 or HDMI 2.1 speeds. Consequently, driving 4K displays at 60 Hz, 120 Hz, or utilizing HDR over an HDMI connection typically requires an active DisplayPort-to-HDMI adapter, regardless of whether the computer's port supports DP++.