My understanding is that you will need an active adapter.
The vga protocol is an analogue display protocol that is designed to drive a crt display directly (ignoring some amps) . The protocol has a few clocks (such as pxclk , lsp, vsync etc...) as well as rgb intensity (3 signals) and positioning which drives x,y mag fields for the electron deflection.
DVI, HDMI and display port are all digital protocols. They deliver a header along with what is essentially a rgb bitmap as well as some clocks and power. There is also some generic signaling possible for things like copy protection and remote command pass though.
Because the standards are so similar the devices can find a common signal level protocol so passive adapters are possible but only at the lowest quality of the source, sink, and both interfaces. All will do 1080p@60Hz. There may be some requirement to level shift on the electrical level and obviously a change has to be made at the mechanical level.
DVI (but not dual link DVI) also has a legacy analogue mode which allows it to be connected via a passive adapter to a vga port. This functionally is a feature of dvi and going dp>dvi>vga won't work as there is no way for the signal to be created. Similarly HDMI as a "media" (and not display) protocol includes a digital audio line but any set up which is not pure HDMI will not have this functionality.
Ben
==============================
This is a summary some aspects are intentionally wrong in order to simplify, other areas may be incorrect due to my ignorance or poor memory. This has been written all from memory with no sources if this information is mission critical or you just don't like being wrong you should cross check, look up format specs on the net or go to the library (the one in the centre is quite good). I provide this information in good faith but accept no responsibility for action taken due to it ;-) .
==============================
On 27 February 2016 13:21:53 GMT+00:00, "Chris. Aubrey-Smith" <cas194@???> wrote:
>My understanding is that rather more is required to achieve the
>digital/analogue conversion.
>
>Chris
>
>
>
>On 27 February 2016 at 13:06, john <jee@???>
>wrote:
>
>> Hi
>>
>> My Understanding is that HDMI is VGA plus audio. So HDMI to VGA
>should
>> work fine. Only difficulty is that some adaptors have difficulty
>with
>> plug and play detection, but that is not a problem because you can
>set
>> the VGA size in the computer.
>>
>> John Eayrs
>>
>> On Sat, 27 Feb 2016 07:17:06 +0000
>> Lisi Reisz <lisi.reisz@???> wrote:
>>
>> > Jeffrey Best will be talking to us about ""Developing a CouchDB
>> > Application Using CouchApp"?, about which more anon. But
>meanwhile,
>> > we have a connection problem. Jeffrey has a laptop with a
>> > DisplayPort port. He also owns an HDMI adapter for it. So we need
>> > to be able to adapt: ideally, DisplayPort to VGA for the
>projector;
>> > failing that HDMI to VGA, but I have an inbuilt unease about a -> b
>> > -> c adaptation. Too much to go wrong! So can anyone help with
>> > DisplayPort to VGA? And a backup of HDMI to VGA? It would help if
>> > solutions are known to work. Jeffrey himself has in fact got a
>> > DisplayPort to VGA adapter, but it doesn't work in practice.
>> >
>> > Jeffrey will bring his presentation on a USB stick in case , so
>could
>> > we be sure to have at least one laptop running LibreOffice Impress,
>> > with an ability to connect to VGA.
>> >
>> > All help and suggestions welcome. If DisplayPort is the future,
>this
>> > problem will arise again, so we need a solution.
>> >
>> > I was thinking of buying this for the group:
>> >
>>
>http://www.amazon.co.uk/DisplayPort-Display-Adapter-Convertor-Macbook/dp/B017Q8OCSY/ref=sr_1_16?ie=UTF8&qid=1456556516&sr=8-16&keywords=DisplayPort+to+VGA+adapter
>> >
>> > until I saw this:
>> > "Didn't work on my set-up, but this due to DP/HDTV not the cord
>> > itself. I needed active adapter I eventually sussed." in the
>reviews.
>> >
>> > So: comments? Advice? Has anyone got an "active adapter"?
>> >
>> > If nothing else offers, I'll get two adapters - DisplayPort to VGA
>> > and HDMI to VGA and hope for the best!
>> >
>> > Lisi
>> >
>> > Lisi
>> >
>>
>>
>> --
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>>
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