Event Handling

This page covers the K3/K3S auto-information (AI) system, which allows the radio to push status changes to your application in real time. Understanding AI modes is key to building responsive software without resorting to constant polling.

For complete command syntax and all parameter details, see the K3/K3S/KX3/KX2 CAT Command Reference.

1. The Auto-Information System

The K3 can notify the computer when the operator changes settings on the front panel. This avoids constant polling and lets your application react immediately to operator actions.

AI Modes

The AI command selects one of three notification modes:

• AI0 (default): Radio sends nothing unsolicited. You must poll for every piece of info.
• AI1: On any front-panel change, the radio sends the IF response (the all-in-one status string). Simple but less granular — you must parse the IF response to determine what changed.
• AI2 (recommended): On a front-panel change, the radio sends the specific response for what changed. If the operator changes frequency, you receive FA00014200000;. If they change mode, you receive MD2;. Much easier to handle programmatically.

Tip

Use AI2; for most applications. It provides specific, targeted updates without the overhead of parsing the IF mega-response on every change.

2. Event Flow with AI2

The following diagram shows how AI2 mode delivers targeted events for each front-panel action:

Key behavior:

• Auto-info responses are sent only for changes made via front panel (knobs, buttons).
• Changes made via CAT commands from the computer do not trigger auto-info responses.
• This prevents echo loops: PC sends command, K3 changes, K3 does not send a response back.

Note

The no-echo behavior is essential. Without it, a computer-initiated frequency change would trigger an auto-info response, which your software might interpret as a new operator change, potentially creating an infinite loop.

3. Polling Strategy (AI0)

When using AI0 mode (polling only), you must explicitly request every piece of information:

• Poll at a reasonable rate: 5—10 times per second is typically sufficient.
• Don’t flood the serial port — the K3 has a limited command buffer.
• Common polling pattern: cycle through FA;, MD;, SM;, TQ;.

Loop every 200ms:
  FA;    → read frequency
  MD;    → read mode
  SM;    → read S-meter
  TQ;    → read TX state

Caution

Polling too fast (more than ~20 commands per second) can overflow the K3’s serial input buffer, causing missed commands or garbled responses. With AI2 mode, you can poll much less frequently since changes are pushed to you.

4. Handling Unsolicited Responses

When AI1 or AI2 is active, your serial read loop must handle data arriving at any time:

1. Buffer incoming data — responses may arrive mid-command or between your polls.
2. Parse on semicolons — split the input buffer on ; to isolate complete responses.
3. Identify the command prefix — the first 2—3 characters indicate which command/parameter changed.
4. Route to handlers — dispatch to the appropriate handler based on the command prefix.

Pseudocode pattern:

buffer = ""
while connected:
    buffer += serial.read()
    while ";" in buffer:
        message, buffer = buffer.split(";", 1)
        message += ";"
        prefix = message[0:2]
        handle_response(prefix, message)

Tip

Always process all complete messages in the buffer before reading more data. A single serial.read() call may return multiple semicolon-delimited responses if several front-panel changes happened in quick succession.

5. Common Auto-Info Events

The following table lists the most frequently seen auto-info responses in AI2 mode:

Event	AI2 Response	Meaning
VFO A tuned	FA...;	Frequency changed
VFO B tuned	FB...;	VFO B frequency changed
Mode changed	MD.;	Operating mode changed
Band changed	BN..; then FA...;	Band switch + new frequency
Filter adjusted	BW....; or FW.......;	Bandwidth changed
AF gain adjusted	AG...;	Volume changed
Preamp toggled	PA.;	Preamp on/off
TX/RX change	TQ.;	Transmit state changed

6. Combining Polling and Events

Best practice: use AI2 for real-time updates, but still poll periodically for:

• S-meter readings (SM;) — not sent as auto-info
• SWR readings (SW;) during transmit
• Power meter readings (BG;)

These metering values must always be polled since they change continuously and would flood the serial link if sent automatically.

Note

A typical hybrid approach sets AI2; at connection time, then runs a slow polling loop (2—5 Hz) for metering data only. All other parameter changes arrive as unsolicited responses, so there is no need to poll for frequency, mode, gain, or filter settings.

7. The IF Command in Detail

For AI1 mode, all events arrive as the IF response. Its fields (38 characters total):

IF[freq 11][5 spaces][rit offset 5][rit on][xit on][tx][mode][vfo][scan][split][tone][tone#][000];

While AI2 is simpler for event-driven programming, the IF; command remains useful as a single-command snapshot of the radio’s complete state. Send IF; at connection time to initialize all your display fields at once, then rely on AI2 events for ongoing updates.

For the full field-by-field breakdown of the IF response, see the K3/K3S/KX3/KX2 CAT Command Reference.