Displayport Alt Mode Cables

[rickyspanish]

Hi everyone

 

I've gone down a rabbit hole...

 

How can you tell if a type-c to type-c USB cable supports the 32.4Gbbps HBR3 bandwidth requirement for DisplayPort 1.3?

The problem I'm facing is that all type-c to type-c USB cables define their bandwidth as a USB 3.1 Gen X specification.

 

From what I understand, you cannot make a direct comparison between the two since they are alternate modes (i.e., displayport alternate is its own thing, it doesn't use USB 3.1 for its data transfer).

 

It's all so confusing, I think I might be getting a headache. Please help.

 

Thanks!

[jaslion]

Your best bet is charging capable or thunderbolt 3 capable usb c cables. Those have to be higher quality than regular ones so you can be pretty sure those will work.

[rickyspanish]

Yeah thanks, I ended up purchasing a 20gbps passive thunderbolt cable but I wonder if a usb 3.1 gen 2 cable would've sufficed. I'm posting my question over at https://www.displayport.org/faq/#tab-ask-displayport as well. If I get an answer from them, I'll update my post here.

[rickyspanish]

I may have found an answer (from reading VESA presentations I found online): "fully-featured type-c usb cable".

What does that mean? Not 100% sure, but I think this refers to cables that can perform data transfer at USB 3.1 gen 2 speeds.

 

Such cables have four high speed lanes.

• Under USB 3.1 gen 1, one lane has a speed of 5Gbps.
• Under USB 3.1 gen 2, one lane has a speed of 10Gbps.
• Under DP Alternate, one lane has a speed of 8.1Gbps.

USB 3.1 gen X only makes use of two lanes (one RX and one TX).

DP Alt can either:

• use two lanes for a max bandwidth of 16.2Gbps (leaving the other two lanes for USB 3.1 gen X), OR
• use four lanes mode for a max bandwidth of 32.4Gbps (no lanes for USB 3.1 gen X)

 

[rickyspanish]

On 4/12/2020 at 3:37 PM, rickyspanish said:

Not 100% sure, but I think this refers to cables that can perform data transfer at USB 3.1 gen 2 speeds.

Small correction since I don't want to put misinformation out (there's enough of that online already). It seems that any USB type-c to type-c cable that can do data transfer at speeds of USB 3.1 gen 1 (or above) are considered "fully featured". Reference and more information here: https://people.kernel.org/bleung/how-many-kinds-of-usb-c-to-usb-c-cables-are-there