Multi-screen EDID passthrough emulation required

I'm still not getting it, I'm looking for something more thorough than "handles communication differently". HDMI communication can also be interrupted by adapters, docks, and switches: this is why EDID has to emulated. I don't understand why it can not be emulated on DisplayPort, which can also have communication interrupted by adapters, docks, and switches. I've asked this question on a different more technical forum. Feel free to answer there as well. And if you have provide the answer here, I'll answer the question there and link to it.

 

Where did you read this? I don't believe this is true. From Wikipedia,

> A bidirectional, half-duplex auxiliary channel carries device management and device control data for the Main Link, such as VESA EDID, MCCS, and DPMS standards. The interface is also capable of carrying bidirectional USB signals.

Could you explain more? Both DisplayPort and HDMI have a dedicated AUX pin. I'm also looking for a technical reason, but I don't believe this is the technical reason.

 

I haven't gotten a chance to really try out the ConnectPro, yet. I got my hands on one, but it had other problems at first and I haven't had time to swap all the cables a second time and try again.

I have discovered something that can make this much easier to live with on Windows. If you hold down the shift and the windows key (or command key if you call it that) and press a cursor arrow, it moves the top window to another window (in the direction of the arrow). This makes it much easier to sort your windows out when they get shoved onto one monitor (which BTW, Windows does without the aid of a KVM switch -- all it takes is two monitors that don't wake up from sleep in about the same amount of time). Just remember to click on all the windows on the slower monitor just before you put the computer to sleep (so they are on top when they get moved to the other monitor).

I have discovered another solution to the dual monitor issue: Get rid of them and buy one really huge monitor. 4K 32-36" monitors have gotten fairly cheap, now.

 

Evan:

Another way to explain the difference between DisplayPort and the other interfaces (HDMI, DVI and VGA) is that the HDMI, DVI and VGA interfaces send EDID over a separate wire using a slow electrical interface and protocol, much like an old serial port connection (except the wire for it is included in the video cable). This started out that way in VGA when the video signals were analog, not digital. DVI and HDMI kept the same slow signal wire and continued to send the EDID information over that signal wire (even though the video signal has switched to being digital). Displayport got rid of the extra wire and included the EDID information in the video signal. Other things you need to know:

• The signal rates for digital video are around 100,000 to a million times faster than the rate data rate for that single EDID wire wire.
• The actual video signals are all one way: They go from the computer to the monitor.
  
• Originally (at least for VGA), I'm pretty sure the EDID information only went from the monitor to the computer.

So, if one is making a KVM switch, one needs three simple switches to switch the video signals (for Red, Green and Blue) and a digital interface that can read the signals on the EDID wire. They don't have to look at the video signals at all -- just pass them from the currently selected computer to the monitor. Reading the EDID wire is even simpler than supporting USB, which they also have to do. This can all be done with an fairly slow 8 bit microprocessor and some minimal interface logic. In order to get at and modify the EDID information for DisplayPort. A displayport interface must take apart the faster video signals to even see the EDID information and this will require more expensive hardware and a lot more engineering.

 

I see responses in my e-mails but I can no longer see them on the page. It seems the forum limits threads to 20 replies or otherwise doesn't enable pagination. I signed up for an account thinking this may be a limitation of a Guest Account. But even as a member, I can't see the posts after post 20.

 

It's not that I don't believe you but why does Wikipedia clearly have an AUX pin for the DisplayPort pinout and say explicitly that EDID uses the AUX channel? What you're saying keeps on getting repeated on this forum, but I'm wanting to see evidence of it or for this to be explained. I don't believe this is true. From Wikipedia,

> A bidirectional, half-duplex auxiliary channel carries device management and device control data for the Main Link, such as VESA EDID, MCCS, and DPMS standards. The interface is also capable of carrying bidirectional USB signals.

You can see from the pin out AUX is pin 15 and 17. https://en.wikipedia.org/wiki/DisplayPort

 

This is all from 6 month old recollections, but I believe that same Wikipedia article also says the AUX pin has never been used for anything in Displayport. I don't know why they decided to implement Displayport that way -- possibly to save money by not having to implement hardware to connect to the aux pin. All of the decisions like this are driven by cost considerations, because the main focus is for consumer devices, not high end use (aka things like KVM switches). A more likely factor is that Displayport is a subset of the Thunderbolt/USB 3.0 technology (which does not have an AUX pin). The same thing is driving USB 3.0. USB 3.0 is really a totally different technology with a fallback to USB 2.0 provided by separate pins on the connectors (which lets vendors put USB 3.0 connectors on USB 2.0 hardware and claim USB 3.0 compatibility -- the class action lawsuit guys should eventually have field day with that).

If you want to know more, you could look up the difference between LVD and high voltage signalling technology. Everything in the computer world is switching to LVD: PCIe, Thunderbolt, USB 3.0, SAS. If you want to take a really deep dive, look up the standards for displayport and EDID....

If you want a short answer, the big picture is that cheap KVM switches are made with 25 year old technology which is really cheap because it's 25 years old.

 

I quote Wikipedia above which says explicitly it's used for EDID. I do agree that HDMI has a first-mover advantage here, but there must be a technical reason for Display Port switches lacking this very basic functionality. But, it's not because there isn't an AUX channel, there is. And, at least according to Wikipedia, as with HDMI, the EDID travels over the AUX channel.

 

And indeed EDID has to use the aux channel to be able to transmit back to the graphics card from the monitor. The main link channels (for the image data) are unidirectional from the graphics card to the monitor.