Editing Openai/692da612-aac4-800b-80dd-f1568632e2ff (section)

=== This will both blink pin 13 and print messages to Serial so we can tell whether the CPU is running. ===

<syntaxhighlight lang="cpp">void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
  Serial.begin(9600);
  Serial.println("START_TEST");
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);
  Serial.println("HIGH");
  delay(500);
  digitalWrite(LED_BUILTIN, LOW);
  Serial.println("LOW");
  delay(500);
}

</syntaxhighlight>
* Upload it (you already know upload works).
* Immediately open Serial Monitor (Ctrl+Shift+M) and set baud 9600.

Expected:
* You should see lines: START_TEST, then alternating HIGH / LOW every 0.5s.
* The built-in LED should blink at the same time.

If you see Serial output but built-in LED does NOT blink, go to Step 2.
If you see no Serial output even though upload said Done, go to Step 3.

Tell me which of the three outcomes happened.