DisplayPort Expansion Card active

My older (non framework) laptop has a DisplayPort and no HDMI port. In order to connect to external displays with HDMI, I had been using a couple of DisplayPort to HDMI cables.

When purchasing my framework laptop I figured I should order a Displayport expansion card. I could continue using the original cables as well. However, once I got my laptop, I couldn’t get the DisplayPort expansion card to work. I tried out different slots for the expansion card, different OSs - windows and different linux distros and different cables as well ( the cables work fine with my older laptop)

I didn’t realize that there was a difference between types of these DisplayPort to HDMI cables I think the ones I have are “passive” and based on now looking at some comments in this forum, it looks like the DisplayPort expansion card would need an “active” adapter or cable to be able to connect to an external HDMI display - Is my understanding correct ?
or should this conversion to active not be needed ?

Welcome to the forums, AABBCC!

Yes, the active adapter would be necessary. The DisplayPort on your previous laptop was probably DP++, so it would work with the passive adapter.

The Framework DisplayPort expansion card uses USB-C DisplayPort Alt Mode, which has some limitations. According to the USB-C Wikipedia article (scroll down to “Alternate Mode protocol support matrix for Type-C cables and adapters”), active HDMI adapters are compatible with DP alt mode, but passive ones are not.

See this Amazon listing for an example of the kind of adapter you would need. Some of these adapters have DP, others plug into the DP alt mode USB-C port directly (like the first one linked).

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I just realized that I got the notification because you linked to me at some point? Sorry for the duplicate information!

Or, you could just use an HDMI expansion card with a bog standard HDMI cable and avoid converting. It’d be cheaper than an active adapter.

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Thanks @Jacob_Padgett and @Fraoch !

I might end up using the HDMI card with the standard HDMI cable. was just hoping to avoid another cable.

did have a follow up though. From the DisplayPort wiki

Dual-mode is an optional feature, so not all DisplayPort sources necessarily support DVI/HDMI passive adapters, though in practice nearly all devices do

I don’t really know how it works so pls let me know if this doesnt make sense but couldn’t (and shouldn’t) the DP expansion card be made such that it supports dual mode/active mode ?
It seems that something like this is done with the HDMI expansion card anyway (i.e. conversion from alt mode → DP → hdmi) so thought it should be possible

@AABBCC

Unfortunately, dual-mode isn’t supported by DisplayPort Alt Mode, even though most regular DP ports (i.e. straight from GPU or iGPU) support it. If you read a bit farther in the section that you linked, under “Dual-Mode Limitations,” you’ll see this statement:

Unavailable on USB-C – The DisplayPort Alternate Mode specification for sending DisplayPort signals over a USB-C cable does not include support for the dual-mode protocol. As a result, DP-to-DVI and DP-to-HDMI passive adapters do not function when chained from a USB-C to DP adapter.

As far as I know, it wouldn’t be impossible to implement, but I’m not aware of this ever being done. It would be a lot of complexity inside a small expansion card.

I agree that an HDMI expansion card would be best.

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While we’re on the topic of DP/HDMI in a single port, I think this would be pretty rad:

http://www.rego.com.tw/product_detail.php?prdt_id=76

This socket physically accepts DP and HDMI plugs! Someone posted it earlier in one of the expansion card threads.

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Gotcha, ok. Thanks for the prompt responses!

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Basically, for the Framework DisplayPort adapter to have DP++ support, they would need to add an active DisplayPort to HDMI adapter internally and be able to switch between the output of that and direct DisplayPort depending on what is connected (DP or DP++).

DP++ is usually limited to HDMI 1.4 link rates (though I think I’ve gotten HDMI 2.0 link rate from an RX580 but maybe I was using 4:2:0 to get 4K60 so I need to retest that)

I suppose an example of this would be some Thunderbolt docks. Thunderbolt can only transmit DisplayPort so HDMI output, either from HDMI or DP++, must be done by an active adapter inside the dock. The HP Thunderbolt Dock G2 does DP++. It may be a feature that comes with the DisplayPort 1.4 MST Hub that it uses.

I prefer USB-C or DisplayPort output, so I can choose what adapter is used to get HDMI. There are many adapters for each HDMI version, 1.1, 1.4, 2.0, 2.0b, 2.1. You’ll want to choose the one that has all the features that you want to use with your display (2.0b adds HDR and 2.1 adds 4K120 at 4:4:4 using FRL instead of TMDS but should be able to do all the TMDS modes of 2.0b and earlier).

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@joevt Wow, nice answer. Wish I could give multiple likes!