Hi Baak,

thanks for the quick reply!

In terms of the limitations, do you mean that I won’t be able to use the display at 5K but at 4K max, or anything else? Because that is not that important for me 🙂 

Hi Lorex,

Well, you should be able to do 5K @ 30Hz. But more is not possible due to the bandwidth of HDMI 2.0. So that is up to you. 4K60Hz or 5K30Hz. 🙂

Hi Baak,

I ordered it (CAC-1332) a couple of days ago and it came today. Unfortunately, it does not work for me… Does anyone have a clue why? Would highly appreciate the help!

Hi Lorex,

What does not work? Do you get anything on the screen? Try lower resolutions? Found the hidden resolutions by Apple? (I’m not an Apple guy just trowing things in here I’ve read). Does it work with just one screen? without the HDMI 1 connected.

Hi Baak,

when I plug it in it says that the Thunderbolt accessory can’t be used. So I thought that this might be a problem of the MacMini not supporting it. Therefore I tried to connect my xbox One with the adapter and the display still doesn’t show anything… So is there I am thinking either the adapter is damaged or malfunctioning or it does not work with that display (LG Ultrafine 5K). 

It works with 1 screen via USB-C, but it doesn’t work if the only screen is the one with the HDMI adapter. 

If you had an Intel Mac, then you could test various custom resolutions to see if any work.

Does the M1 Mac at least detect the display? If so, then you can use the script at https://gist.github.com/joevt/e862b0088ef58b9144877d01401bcee8 to tell you what timing it’s trying to use.

The DisplayPort to HDMI 2.0b chip that the M1 Mac uses probably doesn’t support 5K width even at 30 Hz. It doesn’t matter anyway without a method to create custom timings.

I have a display that can accept 5K 30Hz over HDMI 2.0 and DisplayPort 1.2 from a RX 580 connected to an Intel Mac mini 2018, but I cannot get RX 580 -> CAC-1331 -> display to work with 5K 30Hz. I assume the CAC-1331 and CAC-1332 use the same HDMI 2.0 to DisplayPort chip.

3840×2160 60Hz, 4096×2160 60Hz, 4096×2304 58Hz all seem to work though.

Is there a firmware update to allow greater width than 4096 with the CAC-1331 or CAC-1332?

I don’t think that the MacMini detects the display. At least it doesn’t seem like it from what I see in in the system report (but maybe I am watching in the wrong place… where would you check this?). 

Also, from what you describe, is there a way to set the standard resolution to a lower resolution, so that when I connect the cable it doesn’t go to 5K?

Or is there another solution?

Also, where do I see if there is a firmware update for the adapter?

Did you connect the USB connector of the CAC-1332? Maybe it’s not getting enough power. Can you connect the USB connector of the CAC-1332 to a dock or hub?

Are you using a USB-C cable with the CAC-1332? Maybe it doesn’t work with a Thunderbolt cable.

When the Mac mini detects a display, it will appear in the Displays system preferences panel. If it doesn’t appear there, then you cannot test different resolutions.

If the display can get detected, there probably will not be a 5K option, since the LG UltraFine 5K display does not have a single tile 5K option in its EDID and there’s no way on M1 Macs to create a custom timing like on Intel Macs.

For firmware update, I guess you need to ask Club-3D tech support if the adapter is supposed to be able to do width greater than 4K or not. If they say it should be able to do width 5K, and your adapter cannot (like mine), then maybe there’s a firmware update.

Club-3D doesn’t say what chip is used. SIIG and Delock have similar adapters that use the LT6711A. It has some USB-C specific features, so maybe that means the CAC-1331 uses a different chip? Anyway, the info for the LT6711A doesn’t say it supports 5K width.

The Lontium website at http://www.lontiumsemi.com/product/list_1849.html has a LT6711GX which can convert HDMI 2.1 to DisplayPort 1.4 with USB-C. It works with DVI1.0, HDMI 1.4 – 2.0b (18 Gbps) and HDMI 2.1 (32 Gbps). It supports resolutions up to 8K 30Hz (or 8K 60Hz with DSC). So I guess if the LT6711 can’t do 5K width, then maybe the LT6711GX can do it.

No, the MacMini doesn’t seem to detect the display over the adapter at all…

Thanks for the infos about the chip and everything! Unfortunately, Club 3D doesn’t respond to support emails so idk about the firmware update.

Sorry, I don’t quite understand what you are about the different chips in the last part… Is there an HDMI to USB-C adapter with that 8K chip? Do you think that will work?

You have an LG UltraFine 5K.

If the current adapter (CAC-1332) can work with the LG UltraFine 5K then it probably only works at 4K width because of the LT6711 chip it uses.

If there was a new adapter using the new LT6711GX chip (I have not found any yet) then you could get 5K width from some HDMI 2.0 sources. The LG UltraFine 5K is limited to 600 MHz pixel clock with a single DisplayPort 1.2 connection, so it would have to be 5K39Hz. Two reasons this might not work:
1) The M1 Mac doesn’t have a method to add custom timings.
2) The M1 Mac mini might not support 5K width from its HDMI 2.0 port (because it uses the MegaChips MCDP2920A4 DisplayPort 1.4 to HDMI 2.0 converter which is also used by the Apple TV and Mac mini 2018 and Radeon Pro 580X MPX module).

If the CAC-1332 is connected correctly (the CAC-1332 is connected to a USB-A port with sufficient power and a USB-C cable that can transmit 10 Gbps to a USB 3.1 gen 2 drive is connected between the CAC-1332 and the display’s Thunderbolt input) and the M1 Mac mini still doesn’t detect a display, then there’s nothing else for you to do.

I made a new thread for discussion of the LT6711GX chip at https://insights.club-3d.com/thread/hdmi-2-1-to-usb-c-displayport-1-4-alt-mode/

For anyone who might still be interested, it seems that the USB-C cable that is used is critical. I was about to declare my purchase of a CAC1333 a failed experiment when I noticed a remark, in a YouTube video that referred to a similar adaptor (https://www.youtube.com/watch?v=w5txt3IEFBY), that the presenter only found one particular cable that worked—he didn’t know why the one he was using worked and others he tried didn’t.

I have accepted that I may not ever get two Apple 27″ Thunderbolt displays to work on my M1 Mac mini, but I also have an LG UltraFine 4K Thunderbolt display (which works fine if connected through either of the mini’s Thunderbolt ports). When I connected the LG display through the CAC1333 to the HDMI port, using the cable that came with the display, nothing appeared to be happening. I connected to the mini via Screen Sharing from another Mac and noticed that the display connection appeared to be in a reset loop—the display was recognised, but almost immediately disconnected, then it was again recognised, then disconnected, and the cycle continued for as long as I wanted to keep watching. That observation didn’t really help me, but I offer it in case it suggests something to someone who’s a bit more in the know about these things that I am.

If I connected the LG display, to either the mini’s Thunderbolt or HDMI port, the latter through the CAC1333 adaptor, using an Apple USB-C to USB-C cable, I saw no activity at all.

After watching the aforementioned video I found another USB-C to USB-C cable, one that had been supplied with a Samsung external SSD. When I used it to connect the LG display to the CAC1333, everything worked as I’d originally hoped it would!

I have no idea what the difference between these cables is. The LG cable has the Thunderbolt symbol on each end, but the others, including the Samsung one that ‘works’, don’t. I can mount the Samsung SSD using either the Apple USB-C to USB-C cable or the Samsung one (I didn’t try with the LG cable), but the Samsung cable is the only one that I could get to successfully connect the LG display through the CAC1333 adaptor to the HDMI port on my M1 mini.

Go figure… although this is not the first time I have been confounded by USB-C cables that look the same but clearly behave differently. USB-C cables are not all created equal…