A new mode, supporting DisplayPort, has been published for the new USB-C standard (Display Monitor Vol 20 No 47). VESA and the USB 3.0 Promoter Group have announced ‘DisplayPort Alternative Mode’; it will enable a USB-C cable and connector to deliver DisplayPort AV performance (up to and exceeding UltraHD resolution); USB 3.1 data; and up to 100W of power.
Alt Mode repurposes some or all of the four USB 3.1 lanes to enable DisplayPort performance. Other signalling in the USB-C connector is used for DisplayPort’s AUX channel and hot plug detection function. A reversible USB-C to DisplayPort converter cable will enable existing DisplayPort products to connect to those supporting Alt Mode on a USB-C connector. Adaptors for DisplayPort, HDMI, DVI and VGA displays will also be available.
DisplayPort uses a similar data structure (packetised) and signal lanes (differential AC-coupled) to USB, so the same circuits and cabled can be used to carry USB or DisplayPort data. Data is transferred at up to 8.1Gbps per lane. DisplayPort 1.3 (Display Monitor Vol 21 No 37) defines this rate, although early implementations are like to use existing v1.2a capabilities (5.4Gbps per lane). A speed of 5.4Gbps on each lane will enable DCI-4k resolutions at 60Hz, with up to 30-bit colour.
All four lanes do not need to be used for the same signal. For example, two could carry DisplayPort signals and two could carry USB signals. The new 5k (5120 x 2880) resolution is supported, but requires all four lanes (although USB 2.0 data could still be carried in this case, using separate dedicated pins).
The USB 3.0 Promoter Group is now working with VESA to ensure that consumers can recognise when Alt Mode is supported on USB-C devices.
Display Daily Comments
Chris has written an analysis of what this move means for the USB and DisplayPort standards, and display connectors in general, in the future. See our Front Page this week. (TA)
