Author Topic: Do USB-C monitors use the USB as a video input?  (Read 1246 times)

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Online Alex Eisenhut

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Do USB-C monitors use the USB as a video input?
« on: October 11, 2021, 02:15:01 am »
I've tried reading the various descriptions but it's not clear to me what the USB-C on these monitors does. It makes sense for a laptop to recognize it as a display device, but would the monitor know what to do with a microscope?

I have one of these generic Chinese USB 3.0 microscopes, model H3, not much info available on it, but it has a USB 3 connection.

Can I plug the microscope to a monitor that seems to use UCB-C as an input and see an image?
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Online ataradov

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Re: Do USB-C monitors use the USB as a video input?
« Reply #1 on: October 11, 2021, 02:21:03 am »
USB-C connector carries multiple different protocols. In case of the monitor, if it claims to be able to display anything over USB-C, it would be using Thunderbolt for the actual signalling. There is nothing from the classical USB is left in this case for the picture transfer.

Typical camera/microscope presents itself as a audio/video device. There is no way that monitor would display anything or even recognize that device. Cameras need to be connected to a real USB host.
Alex
 
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Online Alex Eisenhut

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Re: Do USB-C monitors use the USB as a video input?
« Reply #2 on: October 11, 2021, 02:28:18 am »
Thanks, yeah, something didn't make sense for sure. I guess I'll shop for a microscope with a built-in display or a HDMI output.
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Offline evb149

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Re: Do USB-C monitors use the USB as a video input?
« Reply #3 on: October 11, 2021, 03:06:41 am »
There are different ways to send video over a USB-C type connector which is used for one of the variant modes specified to be able to be used with USB C:

https://en.wikipedia.org/wiki/USB-C#Video_output
https://en.wikipedia.org/wiki/USB-C#Alternate_Mode_2
https://en.wikipedia.org/wiki/HDMI#HDMI_Alternate_Mode_for_USB_Type-C

Using one of these alternate-mode links for some kind of displayport connection or such as stated in those links is quite common for devices like tablets, laptops, chromebooks, fairly high end smartphones to support in the "video source" role, though certainly other kinds of equipment could use it acting as a typical laptop would as a video generating source device which would then talk to a similarly compatible display sink monitor in the usual way.

Also besides the above alternate mode scheme, some USB linked monitors have a DisplayLink IC or similar USB connected GPU peripheral in them which is a normal USB super-speed or high-speed peripheral IC which serves the functions of a basic GPU / display adapter which can itself generate outputs such as HDMI / DVI / DP / VGA / DVI.  As you may imagine these are very basic GPUs and not high performance such as something you'd see implemented as an IGP, PCIE peripheral, etc.
They tend to need special device drivers on the host computer's OS to make use of the USB-IC-GPU.

Tragically a lot of multi-function USB hubs, USB to HDMI/DVI "adapter" devices, video source devices, even monitors are completely unclear as to what input or output mode / protocol / configuration they actually support simply saying "USB-C" as input/output specifying nothing about the video transport mode / parameters.  So one is totally left to guess whether it is using a USB-GPU or some HDMI alternate mode or DP alternate mode and therefore what
the bit rate / bandwidth / resolution / video standard / device driver / cabling supported / required is.
It is quite a mess and leads to situations like yours where one is wondering "what does this thing do?!"
without any clear documentation.

 
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Offline evb149

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Online Alex Eisenhut

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Re: Do USB-C monitors use the USB as a video input?
« Reply #5 on: October 11, 2021, 03:25:11 am »
It is quite a mess and leads to situations like yours where one is wondering "what does this thing do?!"
without any clear documentation.

Yup. Usually I try to figure out things myself but in this case I am baffled.
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Offline Berni

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Re: Do USB-C monitors use the USB as a video input?
« Reply #6 on: October 11, 2021, 06:31:15 am »
Yep this is the reason i find USB-C a complete standardization trainwreck.  :palm:

It is now possible to run almost anything imaginable via USB-C, but there is no way to know if it will actually work until you plug it in and try it since both devices must support that one specific feature out of many in order for it to work. Bringing back the ol phrase "Plug and Pray" despite USB 1.1 being the port that truly pulled us into the "Plug any Play" paradime where things simply worked once plugged in.

The only thing guaranteed by a USB-C port is having USB 2.0 support. All the other features like USB 3.0, USB 3.1 Gen2, HDMI, DisplayPort, Thunderbolt...etc are entirely optional so a host PC may support any combination of these it likes, and its impossible to know which since there is no requirement to place standardised icons for the supported features next to the port.

To make things even more confusing even host machines have the same USB-C port as USB devices. So the new symmetrical cables allow you to connect two host PCs (Where nothing will happen because they expect to see a USB device) or to connect two USB slave devices (Where nothing will again happen because they are both waiting for a host to talk to them)

Your case of a USB-C camera and USB-C monitor combines all these cases of how USB-C can go wrong. As a consumer you would expect this to work because they have the same port and you have a cable that fits both. However the camera is likely a USB 3.0 slave device while the monitor is likely a HDMI/DisplayPort slave device. So its two slaves that will not talk to each other, and even if they did, they do not use the same protocol to talk and thus could not understand each other.
 
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Online Ranayna

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Re: Do USB-C monitors use the USB as a video input?
« Reply #7 on: October 11, 2021, 11:01:15 am »
@Berni: You are hitting all the points why i do not like USB-C. Mechanically that connector might be really good. Well, at least it's better that Micro- or *shudder* Mini-USB. :p

But USB did away with a big principle that mostly held true (PS/2 is the one exception i can think of) in the home PC market: If the connector fits, you can expect it to work. Maybe not at peak performance with Fast Ethernet and Gigabit Ethernet, or USB 2 and 3, but it should still work. Even the analog audio jacks have become smart enough to figure out if what is plugged in is a input or output device. Or at least can be remapped in software.

USB-C with all the stuff it supports did away with that and you need to know exactly what the host, the device, and the cable can support. Any of these components can be the reason for issues.
And to know what each device supports you soon will need to be an expert in pictography :p
"Plug-and-Pray" really is the best expression for the mess that is USB-C.

I wonder how long it will take for the first cheap fake "240 Watt capable" USB-C cable to burst into flame.
 

Offline tszaboo

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Re: Do USB-C monitors use the USB as a video input?
« Reply #8 on: October 11, 2021, 11:31:42 am »
Your case of a USB-C camera and USB-C monitor combines all these cases of how USB-C can go wrong. As a consumer you would expect this to work because they have the same port and you have a cable that fits both. However the camera is likely a USB 3.0 slave device while the monitor is likely a HDMI/DisplayPort slave device. So its two slaves that will not talk to each other, and even if they did, they do not use the same protocol to talk and thus could not understand each other.

It becomes even worse if you add on power delivery. My laptop has Type-C charging, but it just becomes unreliable if that is used. "You know it's like magic, data goes this way on the cable, power goes the other way on the cable", and the connection fails for a few seconds every few hours. I miss the old docking station, which had a hundred pins, and it worked every time. Unless if you disconnected without pressing the button, maybe BSOD if you did that.

With USB-C, what powers what is not that simple. Is the portable monitor supposed to power the camera, or the other way around?
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Offline Berni

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Re: Do USB-C monitors use the USB as a video input?
« Reply #9 on: October 11, 2021, 12:13:01 pm »
Yeah USB-PD is another can of potentially flammable worms.

Rather impressive that they manage to push 100W trough that little cable and connector. But given the sort of quality i seen with USB 2.0 cables does get me worried. I seen microUSB cables that couldn't even hold the 500mA without having the voltage on the end of it sag out of spec.

The direction of power flow is also none at all obvious. It used to be that the host always provides power, now anyone can do anything. You can change a laptop from a USB-C charger, but then plug a phone into that same USB-C port on the laptop and charge the phone from the laptop. All while there is software in the loop of things to decide if a port is going to send out 5V or 20V or anything in between. All it takes to send 20V into a phone designed to take 5V is sending a few commands over the I2C bus for the USB power controller chip.
 

Offline Ultrapurple

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Re: Do USB-C monitors use the USB as a video input?
« Reply #10 on: October 11, 2021, 03:39:40 pm »
I have a range of USB-C cables here with different claimed ratings including 3A and 5A. Is anyone interested in me X-Raying them to see how much metal they actually contain?

(Obviously this won't be a scientifically rigorous market sampling, it's just for indication).
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Offline therwp

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Re: Do USB-C monitors use the USB as a video input?
« Reply #11 on: October 28, 2021, 01:21:36 am »
I have a range of USB-C cables here with different claimed ratings including 3A and 5A. Is anyone interested in me X-Raying them to see how much metal they actually contain?

(Obviously this won't be a scientifically rigorous market sampling, it's just for indication).

Yes!
 


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