Pi Monitors

Normally I have my pi connected to my 1080p monitor but occasionally I want to connect it to an old 1280×1024 monitor which I can do via a HDMI – VGA converter I have.

Is it possible to switch between the two monitors without changing any settings?

I take it you mean auto-detect?
There is a bounty, currently underway, for EDID detection and, hence, auto-detect of monitor.
However, I can’t reliably say that the VGA connection sends any EDID back to the computer, like HDMI and DVI do.

The firmware will auto detect the monitor resolution, provided you haven’t explicitly overridden it in CONFIG.TXT. You will have to manually change RISCOS though to the correct matching resolution.

It works for HDMI→DVI, I’ve not tested HDMI→VGA although in theory it should work if EDID data is passing back.

I ended up changing PreDesk.Configure.Monitor to ReadEdid and a short basic program to change the wimp mode based on the hdmi_mode set in config/txt. Not perfect but as least I only have to change config/txt

However, I can’t reliably say that the VGA connection sends any EDID back to the computer, like HDMI and DVI do.

The monitor (1):

Very old or cheap monitors won’t send any information.
Old monitors (1988 or so) may use the pathetic ID bit scheme (really, what loon thought of taking three pins to specify less-than-1024×768-and-mono, less-than-1024×768-and-colour, or 1024×768-or-better-and-colour?).
More recent monitors will support DDC2 (1998) or E-DDC (2004) which is an IIC protocol interface for reading the EDID block. All of my monitors support one of these, even the CRT from the late ’90s.

The monitor (2):

You need to be sure that the EDID returned by the monitor actually matches the display device and makes sense. I believe this bit ROLtd when they discovered that for some monitors, the EDID is varying degrees of junk.

The computer:

You need to have a computer capable of dealing with this. As far as I am aware, the VIDC/VIDC2 do not have the means to read this information from any connected device.

It works for HDMI→DVI, I’ve not tested HDMI→VGA although in theory it should work if EDID data is passing back.

Possibly depends upon the device. My HDMI→VGA dongle passes the EDID info from the monitor upstream.

Possibly depends upon the device. My HDMI→VGA dongle passes the EDID info from the monitor upstream.

As the OP is about the Pi, provided the device is like your one it should just work with the default CONFIG.TXT

I was using this method with all the Pi’s I had at the London RISCOS Show, the only botch I had to do was install AnyMode so I could fool RISCOS into allowing valid resolutions, the Pi firmware however chose the correct resolution flawlessly.