Connection & Discovery

This page covers the full lifecycle of a K3/K3S serial connection: finding the radio on a serial port, identifying the hardware and firmware, managing the power state, and establishing a reliable session.

For general background on command format and serial port settings, see the Programming Guide overview.

Finding the Radio

Serial Port Discovery

The K3/K3S appears as a standard serial port. The port name depends on the operating system:

• Windows — COM ports (COM1, COM3, etc.). Enumerate with the Win32 SetupDi API or by scanning COM1 through COM32.
• macOS — /dev/tty.usbserial-* or /dev/cu.usbserial-* (FTDI-based KIO3 USB).
• Linux — /dev/ttyUSB0, /dev/ttyACM0, or similar.

To locate the K3 programmatically, iterate through available serial ports and probe each one.

Probing a Port

Send a single semicolon (;) as a no-op probe. The K3 ignores unknown or empty commands without producing an error, so this is a safe way to test whether a K3 is listening:

;           → (no response, but port is valid if no error occurs)

A more definitive approach is to send the identification command:

ID;         → ID017;

The ID017; response confirms a K3 or K3S is connected.

Note

If no response arrives within 500 ms, the port likely does not have a K3 attached. Move on to the next candidate port.

Identification Commands

Once you have found the radio, three commands give you everything you need to know about the hardware.

Radio Model (ID)

ID;         → ID017;

The value 017 identifies the K3 family. The K3, K3S, KX3, and KX2 all return ID017;. If you need to distinguish between them, use the OM command or firmware revision string.

Installed Options (OM)

OM;         → OM AP----T-;

The response contains a nine-character option map following the OM prefix. Each position corresponds to a specific option module. A letter means the option is installed; a dash (-) means it is not.

Position	Letter	Option Module
1	A	KAT3 / KAT3A internal autotuner
2	P	KPA3 / KPA3A 100 W amplifier
3	R	K160RX 160 m receive option
4	S	KRX3 sub receiver
5	D	KDVR3 digital voice recorder
6	N	KNB3 noise blanker
7	-	Reserved
8	T	KXV3 / KXV3A transverter interface
9	-	Reserved

In the example response OM AP----T-;, the KAT3, KPA3, and KXV3 are installed.

Note

The installed options determine which commands are available. For example, sub-receiver commands only function when the KRX3 is present (position 4 shows S).

Firmware Revision (RV)

RV;         → RV02.78;

The firmware version is returned as a dotted decimal string. Some commands require a minimum firmware version, so recording this value during initialization is important.

Power State

The K3 has two power states controlled by the PS command. The rear-panel power switch must be on (providing standby power) for serial commands to work at all.

Querying Power State

PS;         → PS0;    (radio is off / standby)
PS;         → PS1;    (radio is on)

Powering On

PS1;        → (radio begins booting)

After sending PS1;, wait at least 4 seconds before sending any other commands. The K3 performs internal calibration during boot and will not respond reliably until it is complete.

Powering Off

PS0;        → (radio enters standby)

Caution

If the rear-panel power switch is off, the radio has no standby power and will not respond to any serial commands, including PS1;. The rear switch must be on for remote power control to work.

Initialization Sequence

The recommended startup handshake discovers the hardware, enables extended command mode, and turns on event-driven updates.

Step-by-Step

1. Probe — Send ; or ID; to verify the radio is present on the port. If ID; returns ID017;, you have a K3-family radio.

2. Discover options — Send OM; and parse the option map. Store the result so your application knows which features are available (sub receiver, autotuner, voice recorder, etc.).

3. Check firmware — Send RV; and record the version. Certain commands or behaviors vary by firmware revision.

4. Enable extended mode — Send K31; to enter K3 extended command mode. This unlocks additional commands and response formats that are not available in the default K2-compatible mode.

5. Enable auto-info — Send AI2; to activate auto-information mode 2. In this mode the K3 spontaneously sends status updates whenever the operator changes a setting on the front panel, eliminating the need to poll.

Note

If you only need basic Kenwood-compatible CAT commands and do not want extended K3 features, you can skip the K31; step. However, most K3-specific applications benefit from extended mode.

Disconnection

When your application is finished with the radio, clean up the session before closing the serial port:

1. Disable auto-info — Send AI0; to stop unsolicited status messages. Leaving auto-info enabled after disconnecting can cause data to accumulate in the serial buffer.

2. Power off (optional) — Send PS0; if you want to put the radio into standby.

3. Close the port — Release the serial port so other applications can use it.

AI0;        → (auto-info disabled)
PS0;        → (radio enters standby, optional)

Multiple Application Considerations

Caution

Only one application should hold the serial port open at a time. Sending interleaved commands from multiple programs will corrupt both the command stream and the response parsing.

• Virtual serial port splitters — Some operators use software such as LP-Bridge, VSPE, or com0com to share a single COM port among multiple programs (logger, rig control, digital modes). While this can work, be aware that command conflicts are possible if two programs send commands simultaneously or if both enable AI mode.

• KIO3 USB interface — The K3’s KIO3 board provides a single USB serial connection. This is the same port used for firmware updates. There is no second independent serial channel on the radio itself.

• RS-232 vs. USB — The K3 supports both an RS-232 port (directly on the KIO3 rear connector) and USB. Only one can be active at a time; they share the same internal UART.

Next Steps

Continue to Frequency & Modes to learn how to read and set VFO frequencies, operating modes, and filter bandwidths.