Switch monitor command not working to switch from HDMI to DP

[chriscla]

Ok, I need to confess. This is not a question about your code :). I'm working on a similar project using an ESP-32 connected via HDMI (SCL, SDA, Ground) to my Samsung CF791 UW monitor. I can send the VCP 0x60 to switch to either HDMI-1 or HDMI-2. However, switching from an HDMI input to DisplayPort does not work.

I plugged a ilnux computer into the same HDMI input that I'm using and was able to use DDCUtil to switch the input from HDMI to Displayport. I captured the i2c bytes and I'm sending the same sequence.

I'm wondering if you've encountered odd behavior like this? Is it perhaps a voltage thing? I'm using ESP-32 with 4.5k pull up resistors and 3.3v.

[tttttx2]

I have actually encountered similar behavior on a HP monitor. Switching from DP to VGA worked perfectly, however, from VGA back to DP was somewhat buggy and didn't work every time. But sometimes it did.

I didn't investigate the issue further - it might be an issue with my implementation being out of spec, or a buggy implementation on the display. Or maybe some screens ignore ddc input on inactive inputs for some inputs, but not for others.

But please let me know if you find the cause of it, I'm probably missing something here.

(Fun fact, my display does not seem to verify checksums at all, guess they don't care too much about doing it properly sometimes)

[tttttx2]

Short update: I pushed an example with active VGA Signal generation of a black screen a few months back, feel free to try if that helps.

The additional example is not in the library manager release yet but you'll find it here in the repo.

[GMGilson]

I found this excerpt on the wiki page for DDC. Though it might be helpful.

Like modern analog VGA connectors, the DVI and DisplayPort connectors include pins for DDC, but DisplayPort only supports DDC within its optional Dual-Mode DP (DP++) feature in DVI/HDMI mode.

Could be the DP ports you're interacting with arent dual-mode compatible.

Maybe also trying using the DP port through a HDMI-DP converter? (I've been considering just using VGA-HDMI converters to make my bad solder jobs easier)