5

I have the following equipment:

I'd like to be able to connect the laptop to the Dell monitor with a single USB-C cable, and then connect the Dell monitor to the HP monitor with a single DisplayPort cable. This should also charge the laptop. When I do this, though, Windows won't let me set the HP monitor to its full resolution (it just doesn't show anything higher than 1920x1080 in the list). For now all I can do is connect each monitor to the laptop with a separate USB-C cable, which does work, but I would prefer to only connect one cable to the laptop (for convenience). Is there any way?

Robert Siemer
  • 633
matthewk
  • 993

2 Answers2

6

DisplayPort over USB-C often does not have the required bandwidth for more than two 1080p screens. This mainly depends on two factors: DisplayPort version and link configuration (number of DisplayPort lanes).

High Bit Rate 2 DisplayPort (specified in DisplayPort 1.2, what you have) supports up to 5.4 GBit/s per lane.

USB-C DisplayPort Alt Mode features 1, 2 or 4 DisplayPort lanes (but no USB SuperSpeed at 4, only High Speed).

One 2560x1440@60Hz screen requires 5.63 GBit/s, meaning it requires two DisplayPort 1.2 lanes (but only 1 at DP 1.4). Adding a 1080p screen would require another lane, requiring the maximum amount of 4 lanes in the USB-C link.

Your 1080p screen indicates in its specs that it features "USB Type-C (Alternate mode with DisplayPort 1.4, USB 3.1 upstream port, Power Delivery PD up to 65 W)". The description strongly hints at it only using 2 DisplayPort lanes. This is enough for at least two screens of this type. DisplayPort 1.4 doubles the available bandwidth, allowing for more and larger displays.

There is of course a workaround: Thunderbolt. Because it uses a different type of link, it can support (at least) two 2560x1440@60Hz screens over a single cable. The drawback is of course that Thunderbolt docks are very expensive.

user219095
  • 65,551
0

It's about the bandwidth of the usb-c connection. Change the USB settings from USB 3.0 to 2.0, if available, on the 1st monitor connecting to your laptop and see if you can increase the resolution. You may need to disconnect and reconnect the usb-c cable for it to work.

guest
  • 1