When does the pulsein() function start counting?

Question

I have an Arduino Pro mini 3.3V, 8 mHz and I want to use the pulsein() function for a low-going pulse. My question: Does the timer start when the function senses a LOW on the input pin, or when the function senses a high-to-low transition, or either?

Code snippet:

pinMode(3,INPUT); // Signal input to Arduino from pin 2 on LM339  - D3
int pwindow = 6000; // Maximum timeout value for pulsewidth
long pcounterA = 0; // Unfiltered Pulse Width of Channel 1
pcounterA = pulseIn(3,LOW,pwindow);
Serial.print(pcounterA);

Thanks for any help. JT

Answer 1

According the official Arduino Reference: PulseIn

Fragment:

Reads a pulse (either HIGH or LOW) on a pin. For example, if value is HIGH, pulseIn() waits for the pin to go HIGH, starts timing, then waits for the pin to go LOW and stops timing. Returns the length of the pulse in microseconds. Gives up and returns 0 if no pulse starts within a specified time out.