One of the most common problems in the PC ecosystem is the enormous number of different cables we have to deal with, although it is true that today most of these cables are USB or video connections. But can USB cables end up replacing video cables like DisplayPort and HDMI? The USB-C Alt DP interfaces aspire to this.
The USB standard has evolved a lot since its appearance in the late 90s, and with each new generation it has improved its capabilities when it comes to transmitting data, and we cannot forget that it was initially proposed as an input and output interface for peripherals. that did not need a lot of bandwidth such as printers, mice, keyboards, etc.
With its version 2.0, its bandwidth increased from 12 Mbits / s to 480 Mbits / s, so it managed to reach the speed of the IEEE-1394 port, better known as Firewire. The consequence of this was the disappearance of said port, and finally with the appearance of USB 3.x it reached speeds of 5, 10 and even 20 Gbits / s, which placed the bandwidth of external hard drives with said interface at the same speed as the internal ones via SATA and even beyond.
But a type of connection that until recently had not been threatened in its existence by USB until relatively recently are video output interfaces such as DisplayPort and HDMI, which could disappear in the day to day in our PCs. as many other interfaces have done. Today we will talk about the culprit, the USB-C Alt DP 2.0.
The specification of USB-C Alt DP 2.0
A USB-C Alt DP 2.0 cable is a Type-C USB cable that serves three functions:
- Send and receive data through USB 3.2 type lanes.
- The power supply of the device from the USB cable.
- Send video data through the DisplayPort 2.0 protocol.
Given that USB-C Alt DP is a variant of USB-C, first of all we have to understand how this interface works by looking at the pins of this type of connection and what function each of them is assigned:
| Pin | Name | Function |
|---|---|---|
| A1 | GND | Electrical power supply |
| A2 | TX1 + | Alternate mode or USB 3.2 |
| A3 | TX1- | Alternate mode or USB 3.x |
| A4 | VBUS | Electrical power supply |
| TO 5 | CC or VCONN | |
| A6 | D + | USB 2.0 interface |
| A7 | D- | USB 2.0 interface |
| A8 | SBU1 | Alternate mode |
| A9 | VBUS | Electrical power supply |
| A10 | RX2 + | Alternate mode or USB 3.x |
| A11 | RX2- | Alternate mode or USB 3.x |
| A12 | GND | Electrical power supply |
| B1 | GND | Electrical power supply |
| B2 | TX2 + | Alternate mode or USB 3.x |
| B3 | TX2- | Alternate mode or USB 3.x |
| B4 | VBUS | Electrical power supply |
| B5 | CC or VCONN | |
| B6 | D + | USB 2.0 interface |
| B7 | D- | USB 2.0 interface |
| B8 | SBU2 | Alternate mode |
| B9 | VBUS | Electrical power supply |
| B10 | RX1 + | Alternate mode or USB 3.x |
| B11 | RX1- | Alternate mode or USB 3.x |
| B12 | GND | Electrical power supply |
To transmit data at high speed, USB-C uses 4 different paths which are: TX1 + – → RX1 + , TX1- → RX1- , TX2 + → RX2 + and TX2– → RX2 -.
Well, in alternate mode we can replace these high-speed data paths as one of the 4 lanes of the DisplayPort protocol video transmission standard and therefore transmit video sacrificing those data lanes and that pins D + and D- ( USB 2.0) are responsible for transmitting data.
Because each USB 3.2 lane has a bandwidth of 20 Gbps and each lane of the DisplayPort 2.0 standard has that same bandwidth, it is possible to transmit video through DP 2.0 in all its glory, and this means being able to reach resolutions of 8K at 60 frames per second with HDR-10, more than enough to cover all needs, as this equates in bandwidth to 4K at 240 FPS.
On the other hand, since data can continue to be transmitted through the D- and D + pins and the power pins remain intact, it is possible to consider scenarios in which a screen can be connected to a PC and does not require external power beyond that the one that gives you the cable itself, so it is likely that in the future it will be your graphics card through a USB-C Alt DP port who will be in charge of powering the screen you are using.
An example similar to this is the Oculus Link cable to connect the Oculus Quest 1 and 2 to the PC, and is that after all a virtual reality headset is nothing more than a screen glued to the face. But it is not the only application, because for example we can have a tablet with this type of interface that we can turn into an additional screen to use in our applications.
In general, the interesting thing is that the USB-C Alt DP in the future allows us to reduce the number of cables on our desk, completely eliminating the need for a power cable for our screens.
If it’s the future, how come NVIDIA removed it from the RTX 3000?
What NVIDIA has removed is the VitualLink that, although it is a variant of the USB Alt DP for virtual reality units, has been rejected by all manufacturers of units of this type so it is not a variant that has much future, more when a few months ago the USB Alt DP 2.0, which we have been commenting on in this post, appeared as a VESA standard. This means that NVIDIA has not had time to integrate it into its GeForce Ampere graphics cards but everything indicates that the AMD RX 6000 will have a port of this type if the rumors are correct.
Mixed mode USB C Alt DP interface
We have the possibility to use only 2 of the USB lanes as 2 DisplayPort lanes instead of the 4.
This cuts the available bandwidth for DisplayPort in half, but at the same time allows 2 lanes to be used for high-speed data sending and receiving, making the monitor a USB hub from which to communicate. Do you want to connect to the graphics a solid disk that you can access directly either for professional rendering or in games? This is another of the existing possibilities.
Will we see DisplayPort and / or HDMI being replaced by USB Alt DP 2.0 or will it all end in a tech anecdote? Only time will tell.