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iemcj

macrumors 6502
Original poster
Oct 31, 2015
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I'm pretty excited that the new imac has decent gaming potential. I have a vizio tv that supports Variable Refresh Rate between 24-120fps and would LOVE to be able to use that for gaming. I was on amazon and couldn't find any cables though that support hdmi 2.1 out, is this just too early or am I missing something? Thanks!
 
From what I have read, Intel's current ThunderBolt controllers do not support HDMI 2.1 so it's not going to be an option.
 
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I think the only adapter that might qualify is the Club 3D CAC-1085 DisplayPort 1.4 to HDMI 4K120Hz HDR Active Adapter M/F

It requires DisplayPort 1.4 with DSC for best results. The iMac 2020 with an AMD Navi GPU should be capable - Nvidia RTX in Windows is also an option.

If you do try it out, post the result of
/System/Library/Extensions/AppleGraphicsControl.kext/Contents/MacOS/AGDCDiagnose -a > AGDCDiagnose_a.txt 2>&1

Any Thunderbolt 3 device or dock that uses a Titan Ridge Thunderbolt 3 controller should be able to support DisplayPort 1.4.

You'll need an HDMI 2.1 cable (48 Gbps).

You many need a USB-C to DisplayPort 1.4 adapter if you connect directly to a Thunderbolt port of the iMac, or if you connect to the Thunderbolt port or USB-C port of a Titan Ridge based (DisplayPort 1.4) Thunderbolt 3 dock.
 
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Just want to comment that a Thunderbolt 3 -> DP1.4 -> CAC-1085 HDMI 2.1 combo didn't work for me. Black screen, couldn't get any signal. Thunderbolt 3 -> DP1.4 worked, and DP 1.4 -> HDMI 2.1 worked with some issues, but when you go TB3 -> DP 1.4 -> HDMI 2.1 it didn't work at all.

Unless anyone has strong evidence of this working somewhere, I think it's wait for a future solution to arrive.
 
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Just want to comment that a Thunderbolt 3 -> DP1.4 -> CAC-1085 HDMI 2.1 combo didn't work for me. Black screen, couldn't get any signal. Thunderbolt 3 -> DP1.4 worked, and DP 1.4 -> HDMI 2.1 worked with some issues, but when you go TB3 -> DP 1.4 -> HDMI 2.1 it didn't work at all.

Unless anyone has strong evidence of this working somewhere, I think it's wait for a future solution to arrive.
You didn't say what hardware you have.
What is your Thunderbolt 3 source?
What is your DP 1.4 source?
Does either source support DSC?
 
You didn't say what hardware you have.
What is your Thunderbolt 3 source?
What is your DP 1.4 source?
Does either source support DSC?
I tried this with a ASRock Creator x570 using onboard Thunderbolt and an RX 570 for the DP.
I also tried it with an HP G2 Thunderbolt dock, as well as Thunderbolt direct out of an HP Laptop.
I don't think any of those combos supported DSC.

If the idea is that the CAC-1085 ONLY works with DSC, that sounds like it would be problematic. My belief is it works both with and without DSC.

Forget about DSC, and even HDMI 2.1 for a second.

Just outputting a simple 1080P non DSC HDMI signal should be able to go from TB3 -> DP1.4 -> CAC-1085 -> HDMI input on HDTV and work. It didn't when I tested it.

I only bring this up because I had the expectations that someone could buy a 2020 iMac with an RX5700 or higher and use the TB3 to output 8K HDMI 2.1, and so far I don't see a way to do that.
 
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I tried this with a ASRock Creator x570 using onboard Thunderbolt and an RX 570 for the DP.
I also tried it with an HP G2 Thunderbolt dock, as well as Thunderbolt direct out of an HP Laptop.
I don't think any of those combos supported DSC.

If the idea is that the CAC-1085 ONLY works with DSC, that sounds like it would be problematic. My belief is it works both with and without DSC.

Forget about DSC, and even HDMI 2.1 for a second.

Just outputting a simple 1080P non DSC HDMI signal should be able to go from TB3 -> DP1.4 -> CAC-1085 -> HDMI input on HDTV and work. It didn't when I tested it.

I only bring this up because I had the expectations that someone could buy a 2020 iMac with an RX5700 or higher and use the TB3 to output 8K HDMI 2.1, and so far I don't see a way to do that.
I think the adapter should output something even if DSC is not available. Is the adapter's USB power connected to a USB-A port that has power?

I have the same adapter. It works for 4K 60Hz from DisplayPort 1.2 of my Mac mini 2018 to Acer XV273K display.
 
I think the adapter should output something even if DSC is not available. Is the adapter's USB power connected to a USB-A port that has power?

I have the same adapter. It works for 4K 60Hz from DisplayPort 1.2 of my Mac mini 2018 to Acer XV273K display.
Glad it worked for you! Now you're making me think I may have just gotten a defective one. I did have it powered via USB. I returned it or I would test further.
 
Thunderbolt 3 -> DP1.4 worked
Hey, you said here that "it worked" using Thunderbolt 3 > DP1.4. Did you mean that you managed to get 4k @ 120hz from a 2020 iMac?

I'm trying to get a 2020 iMac with a 5700 XT connected to a 120Hz monitor (the Asus PA32UGC). This forum thread here is as close to evidence that I've seen suggesting it might be possible - but it's not super clear what you mean that "it works".

And if it did work, which specific cable and dongles did you use?

Thanks in advance!


As a side note: one of the few places I've seen listing compatibility is this site; https://tonsky.me/blog/monitors-mac/ I've reported my disappointing findings so far but will add more if I can get a DP1.4 solution working.
 
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