MM M1: always 2 displays available in some circumstances

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majortom1967 Author

Level 3

636 points

MM M1: always 2 displays available in some circumstances

Hi.

I'm using 2 displays attached to my MacMini M1. One for work and one for gaming. The first is via HDMI and the second is via usbc-DP. If only the first is switched on I just see it connected (pict 2); if only the second is on I can see both connected (pict 1) even if the first is switched off. Shouldn't be a problem for general management (regardless messing up desktop's background) and gaming performance but... is this normal?

(Monterey 12.0.1)

TNX

Simon

Mac mini, macOS 12.0

Posted on Nov 18, 2021 6:24 AM

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Answer 1

Best reply

Luis Sequeira1

Level 9

65,288 points

Nov 18, 2021 8:18 AM in response to majortom1967

I have an HDMI monitor attached to my MacBook Pro 16".

If I turn it off, I still see it in System Preferences->Displays, and I can still move the cursor out into the area where it is supposed to be. I can still move windows to the display. For purposes, the mac treats it as if it were "live".

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Answer 2

Nov 18, 2021 8:40 AM in response to majortom1967

I would not call it unacceptable.

This may be how HDMI works.

There is some signal coming over the HDMI cable, even if the display is turned off.

You can try this very simple test.

With the display turned off, connect the HDMI cable to your mac.

Your mac will immediately detect the display because the cable is still "live".

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Answer 3

Nov 19, 2021 6:25 AM in response to majortom1967

My interpretation of this situation is that the display is not “completely off”

Try these experiments:

1) plug the cable on the mac end but NOT on the display. Does your mac react like a display was added - like going black, changing resolution, and indicating two displays? If so, then you will have confirmed a bug on the mac side.

2) instead of just turning the display off, try removing power from it (if necessary, by removing the power cable). Does your mac STILL work like the display is connected?

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Answer 4

majortom1967 Author

Level 3

636 points

Nov 19, 2021 6:50 AM in response to Luis Sequeira1

Tnx.

There's something on the HDMI side as detaching the cable either from the Mac or from the primary display everything works as it does. And neither disconnecting the primary display from the power surge changes something as it still behaves as the primary display (i.e.: selecting System Preferences from the secondary display results in having its windows still in the primary display).

Only a restart works. Therefore, I'm thinking there a sort of memory about the HDMI display somewhere.

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