UP2516D, daisy chain, DisplayPort issue

Question

Dear Sir or Madam, I recently faced a very strange issue with my computer, which solution was finally the DisplayPort cable. To have this issue documented for the later generation, I would like to dig deeper and want do some research, why and what has caused the problem at the first place. My computer consists of two 25'' (Dell UP2516D) Monitors on daisy chain, both ofc run at 10bit mode. Both at full native resolution. Screen and picture are perfectly set up. Due to some ergonomically matter, I had to extend the DisplayPort cable which come from the graphics card and goes to the first screen. So I bought a 3m DisplayPort to Mini DisplayPort/Thunderbolt cable from the German Cable manufacturer Kabeldirekt. So far so good, I reconnected everything, and the picture was fine. Later, I also upgraded some parts in my computer, and now comes the strange thing. The newly installed part (water cooling), was partly fault and I had to reset that change, so back to the old water cooling. But then, I had no picture and or the screen stayed black. However, a boot after the computer had been shut off correctly, the mainboard faulty check hang at DRAM, which means the graphics card or the ram have an issue.  But, after I did a cold start (power cord off, power supply off/on) picture was back on and pc ran normal. My bios had been reseted for some unknown reason, even the my mainboard manufacturer cannot say what the reason is. So I did a mem-test, all good, no error.Tested the Graphic card. Reseated the pump several times. Tested with a different PSU.Everything was replaced and tested. By accident I stumbled upon some similar issues on a tec-forum. And the suggestion was the solution for my issue. So i used a old/other, stock displayport cable, (bc the cable was longer). But it doesn't make any sense for me. Because the extend cable was also 1.2 and was supporting up to '4k'. The only thing that I got told by the manufacturer, was that the cable only supports 8bit but 10bit. The older stock cable, is one from my old Monitor from 2010/11. Some details on that cable:Kabeldirekt, Displayport cable, E358026, AWM Style 20276, 80°C, 30V VW-1Stock(Dell) cable: Displayport cable, E344977-E, AWM Style 20276, 80°C, 30V VW-1 COXOCCurrent stock HP cable: Displayport cable, E164571, AWM Style 20276 80°C, 30V VW-1 BIZLINK Technology So my question is, are there any difference between certain displayport cable within the same version? 1. What is the recommended voltage that a daisy chain setup need?2. How much or what voltages, if so, must the cable support a fault-less working?3. And how to know that when buying cables?4. What must a third party cable need to support for a daisy chained setup? MST must be available on the device (monitor), ok,  but there are no such requirements for cable. Many thanks for your help! Best regards!Kasun Dewasurendra

jphughan · Accepted Answer

@K.Dee  happy to help!  DisplayPort 1.4 is the current standard because DisplayPort 2.0 hasn't launched yet.  I would recommend getting a single cable of the required length whenever possible rather than using couplers or extensions.  Yes, using cables that are tested to a higher standard than your use case requires will certainly increase the likelihood that everything will work even if you introduce couplers or extension cables, but it's still not a guarantee.  By comparison, if your use case only requires DisplayPort 1.2 and you buy a single cable of the required length that's rated for DisplayPort 1.2, then you can expect it to work (unless it's a defective cable or a shoddy manufacturer overall).  If you can't find a cable of the required length that's rated to the standard you require, then it might be because current cable manufacturing technology simply doesn't allow the required signal integrity to be maintained along the cable length you're trying to use.  For example, right now USB-C cables that support USB 3.1 Gen 2 are limited to 3 feet, and Thunderbolt 3 cables that support 40 Gbps are currently limited to about 18 inches, unless you go with active cables, in which case you can reach up to 6 feet.

DELL-Chris M · Answer

The UP2516D DP MST daisy chain was only tested/verified with our Dell OEM 05VX0 1.8M mDP to DP cable.

That E number (E344977-E) other Dell monitor cable is not present in the Dell part tool? Is there a Dell 20 digit serial number on it? What other Dell monitor model?

K.Dee · Answer

Hi

Thanks for the reply.

The UP2516D DP MST daisy chain was only tested/verified with our Dell OEM 05VX0 1.8M mDP to DP cable.

Understood, however I currently don't have the Stock Dell cable hooked up, bc its simply too short.

That E number (E344977-E) other Dell monitor cable is not present in the Dell part tool? Is there a Dell 20 digit serial number on it?

Unfortunately there are no other numbers on the cable or namings on the cable.

Stock Dell Monitor Cable

What other Dell monitor model?

Both are the same model (2x UP2516D)

Screen is however prefect, no lag, no flickering what so ever, with the stock Dell or now with the slightly longer stock HP cable.

Dell OEM 05VX0 1.8M mDP to DP

What are the specifications for this cable, I'm afraid I need at least a 2m cable.

Thanks

BR

Kasun

DELL-Chris M · Answer

2M or longer was not validated by Dell. All I know is that the 1.8M cable was made by Wistron.

K.Dee · Answer

Got it! Are there limitations when i use a coupling adapter so that i use 2 same type cables? Thanks!

DELL-Chris M · Answer

Unknown, we have never tried this.

jphughan · Answer

@K.Dee coupling adapters can always be risky to use, especially when you're trying to send a signal that will already require near maximum performance from the cables you're using. The reason is that the transition between a male connector and a female port is actually a source of significant signal strength loss. Using an extension cable introduces one more of those transitions in the overall cable run, and using a coupler introduces TWO more of those transitions. So the result is that even if each individual component is rated to the specification you require for your use case, the overall assembly might not perform up to that specification anymore. You're more likely to encounter this when using lower quality components that may have only barely performed to specification and/or when your use case has requirements near the top end of the specification's capabilities.

This "transition loss" is incidentally why active cables exist, especially with HDMI cables and Thunderbolt 3 cables. They incorporate signal booster chips on one or both connector ends of the cable. In the latter case with an HDMI cable for example, that means that the HDMI signal gets boosted by that chip immediately after it incurs a signal strength loss by crossing over the first transition (exiting the system connector and entering the cable) and then gets boosted AGAIN just before it's about to incur a second signal strength loss on the second transition (exiting the cable and going into the display input connector). This is why active cables can support a given signal through much longer cable runs than passive cables -- and why they cost more. But typical couplers and extension cables aren't active.

K.Dee · Answer

Thanks for the very technical explanation!

I found this page . https://k.kramerav.com/support/bwcalculator.asp

Which shows the theoretical output of a channel, with my settings.

So in my case it should be enough if i just jump a version or two ahead and buy a 1.4 cable, which covers the bandwidth in total.

Monitors

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