Exploring DisplayPort Alt Mode over USB-C
DisplayPort Alt-Mode
DP Alt-Mode, or DisplayPort Alt-Mode, was initially introduced by the Video Electronics Standards Association (VESA) in 2014. It enables the transmission of DisplayPort protocol signals over a USB-C connector. The DisplayPort signal utilizes the four SuperSpeed differential pairs within the USB-C interface to transmit DisplayPort data packets up to HBR3 (High Bit Rate 3) mode, featuring 8.1 Gbps per DisplayPort Lane. Depending on the number of DP lanes it utilizes, there are typically two modes of DisplayPort Alt-mode, 2-lane, and 4-lane mode.
2-Lane DP + USB 3.2 Mode:
This mode utilizes 2 lanes of HBR DisplayPort signal along with 1 lane of USB 3.2 signal, enabling support for either one 4K UHD Display (3840 x 2160) at 60Hz or two 2K (2560 x 1600) displays at 60Hz. USB data transfer speeds can reach up to USB 3.2 Gen 2x1 at 10Gbps simultaneously with the display. This mode is commonly adopted by USB-C docking stations to facilitate both DisplayPort and SuperSpeed USB data transfer.
4-Lane DP + USB 2.0 Mode:
This mode utilizes all four SuperSpeed differential pairs for 4 lanes of HBR DisplayPort signal, doubling the maximum DisplayPort bandwidth compared to the 2-lane mode. It allows for either two 4K UHD displays (3840 x 2160) at 60Hz or four 2K (2560 x 1600) displays at 60Hz. However, only USB 2.0 signal is supported in this mode. It is often utilized by USB-C monitors and portable displays, which typically only require USB 2.0 for keyboard, mouse, or touchscreen control.
Passive USB-C cables typically support both DP Alt-Modes, while active USB-C cables lack automatic detection and mode switching support. Users should be attentive when selecting these cables to ensure the best support for their applications.