LG M3704CJ Owner's Manual page 61

Controlling the Multiple Product
RS-232C
Transmission / Receiving Protocol
03. Aspect Ratio(Command : c) (Main picture format)
To adjust the screen format.
You can also adjust the screen format using the ARC
(Aspect Ratio Control) button on remote control or in the
Screen menu.
Transmission
Data 1 : Normal Screen (4 : 3)
2 : Wide Scran (16 : 9)
4 : Zoom (AV)
6 : Original (AV)
7 : 14 : 9 (AV)
9 : Just Scan (HD DTV) * When the RGB, HDMI / DVI PC mode(1:1)
10 to 1F : Cinema Zoom 1 to 16
B : Full Wide
Acknowledgement
04. Screen Mute(Command : d)
To select screen mute on / off.
Transmission
Data 0 : Screen mute off (Picture on)
1 : Screen mute on (Picture off)
Acknowledgement
A6