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Trying to hook my Macbook Air M2 to a Sharp PN-K321 with USB C to DisplayPort cable but only getting 30hz. Shouldn't this combo be able to do 3840x216

cedarm

cedarm

macrumors newbie
Original poster
Jul 22, 2022
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Hi all,
I have a M2 MacBook Air, and I'm trying to get 3840x2160 @60hz out of my new to me Sharp PN-K321 display which I got second hand. This monitor, as I understand it, is capable of it, and so is the M2. I bought a cable from Amazon that I thought would do the trick (no link so I don't get in trouble but the product title is:

USB C to DisplayPort Cable [8K@60Hz, 2K@240Hz], uni USB Type C to DP 1.4 Cable 6ft, [32.4 Gbps, Thunderbolt 3/4 Compatible]

but no joy, only getting 30hz. I reset the monitor to factory defaults, but otherwise, all I've done is plug it in, and fidget around in the MacOS display control panel. I'm able select various scale options, but 30hz is the highest available.

Any tips or tricks? Where am I going wrong? Thanks in advance!
 
Found this on StackExchange:

"
The StarTech cables work perfectly, all that was required to enable 60Hz was to use the display's onscreen controls to enable MST mode. Restart the display and voila.

Definitely noticeable improvement in scrolling through large Photoshop and Illustrator files."
 
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Thanks for the suggestion. I tried switching to MST mode, and this gave me 60Hz, but unfortunately only at 1920x1080.
 
I doubt your monitor has an option for which version of DisplayPort to use, but it's worth a try. Some monitors support both DisplayPort version 1.2 and 1.4 and you can switch between the two. Your monitor is old enough that I doubt that v1.4 was a consideration when it was built.

It's also probably worth a shot to try one more cable.

https://www.amazon.com/DisplayPort-...795217&sprefix=usb-c+to+d,aps,106&sr=8-3&th=1

This one is DP v1.2, but it specifically states that it supports MST (Multi-Stream Transport), so it may do the trick. I looked at some cables with the specs that you showed, but they didn't say that they were MST compatible.

My understanding is that the older 4K monitors were actually treated by the computer as two separate 1920x2160 displays and the data was sent across via two different streams (thus, MST) and then the monitor displays the two signals side-by-side to give you one image.

This cable isn't guaranteed to solve the problem, but if you have a few bucks to spare, I'd give it a try.
 
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Welp. Tried that cable, and it didn't work. Thanks for the suggestion.
 
I don't think MacOS supports DisplayPort-MST modes unfortunately. It can do MST but only with the aid of Thunderbolt.

This one might be hard to solve.

If the monitor supports side-by-side input you could possibly output one-half of 1920x2160 on one cable and use a second cable outputting the other half with the help of a DisplayLink adapter.

This would likely be more wonky than it's worth, though. Aside from the couple drawbacks DisplayLink brings, MacOS would treat the two halves as two monitors, unless some third party software can help solving that.

I'd switch the monitor because even switching to a mac that doesn't require DisplayLink still would have the "no MST"-issue with that monitor.
 
Sorry that it didn't work out. I guess the monitor is just a bit too old to work with the new modern video support of the M2 MBA.
 
Not the same, but related: To connect a MacBoook Air M2 to a Dell E2216H monitor via its DisplayPort, each of these cables worked for me:
 
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I know this conversation is a bit older, but I was facing the same problem. Also thought it might help somebody else too...

Setup: MBP 2021 (14" M1 Pro), Dynabook TB4 dock, LG 4K 32" monitor via TB/USB-C and Sharp PN-K321 via DisplayPort.

At first I would only get the inferior 2k resolution as options. This thread made me fiddle around with the DisplayPort mode. Setting it to SST solved the issue. I now have all the same settings available as the LG monitor.
 
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