An RS-232 connection lets an external controller send commands to a compatible TV or professional display and receive status information where supported. Power switching and input selection are documented uses, but the available functions depend on the display and its command protocol.
The interface has applications in installed AV systems and service work. Sony describes its serial implementation as a network-independent, one-to-one connection intended for installations requiring reliable control. Samsung says its EX-LINK serial-control port is typically used by service technicians.
Supported commands vary by display
Sony’s command documentation for compatible BRAVIA Professional Displays includes power, input selection, volume, mute and picture-mode controls. Its protocol distinguishes commands that change settings from queries that request information and responses returned by the display.
Those functions have operating limits. Sony lists input selection, volume and mute as unavailable in standby, and notes that input availability varies by model.
Connections and settings depend on the model
Sony documents a 3.5mm stereo mini jack for serial control on supported professional displays. LG’s installation manual for UV3***-U TVs describes nine-pin and phone-jack RS-232C connections, while warning that connection types differ between model series and that not all models support the connectivity described.
A computer or AV control system can serve as the external controller. For the implementation described, LG specifies a crossed cable, 9,600bps, eight data bits, no parity and one stop bit, with commands ending in a carriage return.
Sony likewise says the controller’s serial settings must match the display’s communication parameters; otherwise, commands may not be received correctly. The connection and communication requirements therefore follow the particular display’s documentation.
Power control also depends on the connection. LG’s manual says its power command can communicate when the TV is on or off through an RS-232C cable, but works only while the TV is on when using the USB-to-serial converter connection described in the manual.
Serial control does not distribute video
In these TV-control applications, RS-232 carries commands and responses. Selecting an HDMI input tells the display which input to use; it does not send the source’s audio and video through the serial cable.
Other connections have separate roles. HDMI carries audio and video, while some USB connections can provide power. Samsung, for example, identifies a USB port for powering a hard drive.
An HDMI matrix handles source routing to displays. OREI says its UHD-404 4×4 matrix routes audio and video from up to four HDMI sources to any combination of four displays. The company lists front-panel buttons and an infrared remote as its controls.
