Reading the clock on an Uno

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1

I'm new to Arduino, and logic analyzers. I have an Uno and a Saleae Logic. I can run the blink program and see the signal on pin 13 that cycles the LED. But I'd like to see it in relation to the clock. I've searched around, and though that the clock pin on the Uno is 7, but there is no signal on that pin.

So how do I read the clock signal too?

Thanks.

2

Easy answer: you can't.

Difficult answer: program the 'clock output' FUSE and grab the signal on the 'CLKO' pin (see the datasheet).

I also wonder how accurate that will be. Sampling a 16MHz signal with a logic analyzer that can only do 24Ms/s.

3

Arduino has no build in clock, you could program a timer to give a pulse on a pin or do it manually

try this (not tested)

void setup()
{
  pinMode(13, OUTPUT);
  pinMode(7, OUTPUT);
}

int state = HIGH;

void loop()
{
  if (state == HIGH) 
  {
    state = LOW;
  }
  else 
  {
    state = HIGH;
  }
  digitalWrite(7, state);
  digitalWrite(13, state);
  delay(100);
}
4

Thanks for the responses.

So I basically can only measure pins relative to each other, not to a baseline. At least I know I wasn't missing something.