LG Display RS232 Commands: The ka Power Command, Set ID and the NG Reply

The Format: Two Letters, Set ID, Data

LG's protocol is plain ASCII in three space-separated groups, terminated by a carriage return:

[Command1][Command2] [Set ID] [Data]<CR>

Power on, addressing all sets:

ka 00 01

That is the whole idea. k and a together mean power; 00 is the Set ID; 01 is the value.

The byte-level view, addressing Set ID 01:

ASCII : k  a     0  1     0  1  <CR>
Hex   : 6B 61 20 30 31 20 30 31 0D

This matches the hex string LG's own documentation publishes for power-on (6B612030312030310D), which is a useful confirmation that you are building the frame correctly.

Note the values are ASCII digits, not binary. The Set ID 01 is the two characters 0 and 1 (0x30 0x31), not the byte 0x01. Sending binary here is a common mistake for people arriving from Samsung MDC, which is the opposite convention.

Set ID Rules

Set ID is assigned per display in the OSD menu. The maximum may be lower on a given model.

Using 00 to address everything is convenient for "all screens off at closing", and unlike Samsung MDC's broadcast, LG sets do generally still reply — though with several displays answering at once on a shared bus you should not rely on parsing that.

Command Reference

kf takes a hex value: kf 01 32 sets volume to 0x32 = 50.

Input select is the field most likely to differ from your notes — LG moved from kb to xb across model generations, and the input values differ too. As with every brand, the reliable method is to switch the input by hand and query the current state, rather than trusting a table found online.

Reading the Reply

[Command2] [Set ID] [OK or NG][Data]x

An acknowledged power-on from Set ID 01 replies roughly as a 01 OK01x.

OK versus NG is the useful part. NG means the display received a well-formed command and refused it — which, exactly like Sony's err_cmd, is good news for your cable and your framing. If you are getting NG, stop checking the wiring and start asking why the display is declining.

Which leads directly to the most surprising reason it declines.

The Media Playback Trap

While the display is playing media from USB or internal memory, almost every command is rejected with NG.

The documented exceptions are:

• ka — Power

• kf — Volume

• ke — Mute

• mc — Remote key

Everything else fails until playback stops.

This produces a genuinely baffling field symptom: your control system works perfectly during commissioning with the display on a blank input, then half the buttons stop working once the exhibit content is running. Input switching in particular will appear to break exactly when the hall goes live.

If you are using an LG display's internal player for exhibit content, design your control around those four commands, or drive the content from an external player so the display stays in a normal input state. On a signage install this is a real architectural constraint, not a quirk.

Why Power-On Fails Through a USB Adapter

LG documents a specific and unusual gotcha:

With a real RS-232C cable, the ka command works in both power-on and power-off states. Through a USB-to-serial converter cable, the command works only if the display is already on.

So the classic "power off works, power on does not" symptom on an LG has three possible causes rather than the usual two:

• Standby power mode has disabled the control receiver (the normal cause across all brands)

• You are going through a USB-to-serial adapter (the LG-specific cause)

• Wrong Set ID

If you are commissioning with a laptop and a USB adapter, and power-on refuses to work while everything else does, try a machine with a genuine serial port before changing any display settings. This one is easy to chase for a long time because everything about the setup looks correct.

See null modem vs straight-through for more on USB adapter pitfalls.

Enabling RS-232 on an LG

Serial control has to be available in the first place. Two things to check:

Commercial displays generally have RS-232 active by default, but confirm the Set ID is assigned and that no competing control mode is enabled.

Consumer TVs vary widely. Many LG TVs expose serial control only after enabling it in a service or installation menu, and some models simply do not have a usable serial port despite having the connector. If you are building a permanent installation, verify serial control works on that exact model before committing to it — this is the recurring argument for commercial panels over consumer TVs in exhibition work.

Model variation is real: different LG monitors use different commands, so check the RS232C manual for your specific model rather than assuming one table covers the range.

Wiring and Serial Settings

Pins 2 (RXD), 3 (TXD), 5 (GND), crossover — the standard three-wire null modem.

One field report worth flagging: at least one integrator found commands worked only without a null modem between two adapters — which is a reminder that when you stack an adapter, an extension and a crossover, you can end up crossing the signal twice and undoing it. When in doubt, meter the end-to-end path rather than reasoning about the individual pieces.

Why Your LG Command Gets No Response

1. NG returned — the display is playing media. Only ka/kf/ke/mc work in that state.

2. Power-on only, through a USB adapter. See above.

3. Wrong Set ID, or Set ID not assigned on the display.

4. Wrong command for the model generation — kb versus xb for input.

5. Sent binary instead of ASCII digits. 01 is 0x30 0x31.

6. Missing carriage return. Every LG command ends with CR.

7. Serial control not enabled — particularly on consumer TVs.

With SoftControl

SoftControl sends LG's ASCII frames over serial or TCP, and its command tester shows both the transmitted string and the raw reply — so NG arrives as readable text and you can immediately tell a refused command from an absent one.

For other display protocols see Samsung MDC and Samsung Ex-Link; for cabling see the null modem guide.