Switching input source on LG monitors

This page summarizes what has been learned about switching input on recent LG monitors. These recent monitors no longer support channel switching via the standard setvcp methods.

Some of these monitors might support an alternative and non-standard channel to switch the input, namely the service/factory/manufacturer sidechannel "DDC2AB" (0x50 instead of 0x51). This was discovered by @shinyquagsire23. Newer versions of ddcutil have the --i2c-source-addr option to make use of this sidechannel.

An example usage is: ddcutil -d 1 setvcp xF4 x0090 --i2c-source-addr=x50 --noverify The --noverify seems required because the setvcp command on these channels do not report back if the channel switch succeeded.

Theoretically supported

The following monitors are potentially supported with this side channel based on information from the firmware, but require verification: GP850, QP750, GP950, WP950C, QP88D, UL550/500, GP750, 28MQ780, UP850, GP950, UN880, GQ850, UQ85R, WQ75C, WQ60C, WQ95C, UP600, UQ85R again

Explicitly unsupported monitors (according to LG itself): GP850, UQ750, GQ900

Side channel ids:

• x50: Input switching
• x51: PBP controls

Side channel commands:

• xD7: Activate PBP 0xD7
• xF4: Switch input

Side channel PBP values:

• PBP_NONE = 0x1
• PBP_LR_UNK2 = 0x2
• PBP_LR_66_33 = 0x3
• PBP_LR_50_50 = 0x5

Side channel input switch values:

• MONITOR_AUTO = 0x0
• MONITOR_DP1 = 0xD0
• MONITOR_DP2 = 0xD1
• MONITOR_DP3 = 0xD2
• MONITOR_USB_C = 0xD2
• MONITOR_HDMI1 = 0x90
• MONITOR_HDMI2 = 0x91

Sources:

• https://github.com/rockowitz/ddcutil/issues/100#issuecomment-1444483801
• https://gist.github.com/shinyquagsire23/f6b2adef253c6c3ab557a4852bf3abad

Test results

• 27UN850-W, confirmed by @pmfournier

• 27UP850-W, confirmed by @Prototyped

  • x90 = HDMI 1
  • x91 = HDMI 2
  • xD0 = DisplayPort
  • xD1 = USB Type C (DisplayPort alt-mode)

• 29UM69G, confirmed by @jonpas

  • x90 = HDMI (no HDMI2 on this model)
  • xC0 = Display Port (no DP2 on this model)
  • xE0 = USB-C

• 32QN650-B, confirmed by @agspoon

• 32UD99-W, confirmed by @andrewgodman

  • x90 = HDMI1
  • x91 = HDMI2
  • xE0 = Display Port (there's no DP2 on this model)
  • xC0 = USB-C

• 34WN750-B, confirmed by @permezel

  • x90 = HDMI1
  • x91 = HDMI2
  • xd0 = DP1

• 34WN80C-B, confirmed by @nicklan

• 43UN700-B, @benjamingwynn was not able to confirm