I have a DS3231 Real Time Clock module and I'd like to use the Square Wave output.

I wonder how can I set the frequency of the pulse?

How long is the (time) length of the pulse?

I have a DS3231 Real Time Clock module and I'd like to use the Square Wave output.

I wonder how can I set the frequency of the pulse?

How long is the (time) length of the pulse?

UPDATED QUESTION

In order to use the DS3231 as an 1PPS interrupt, I want to use the Square Wave output. Here's how I connected it to an Arduino.

I connected to the SQW output a 10kΩ pull-up resistor and an LED. After that I tested the code which shows the time and worked fine.

#include <Wire.h>
#include "RTClib.h"

RTC_DS1307 rtc;

void setup () {
   Serial.begin(9600);
   #ifdef AVR
      Wire.begin();
   #else
      Wire1.begin(); 
   #endif
   rtc.begin();

  if (! rtc.isrunning()) {
     Serial.println("RTC is NOT running!");
     rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
    }  
  }

void loop () {

   DateTime now = rtc.now();
   Serial.print(now.year(), DEC);
   // etc
   }

(The DS3231 works fine with the DS1307 library)

In this case the LED was just flickering, so I thought that the default frequency of the SQW should be grater than 1Hz. I googled a bit and realized that I had to change some registers. So I found this piece of code which I called from the setup() function, but with no success, the LED is still flickering.

void set1Hz() {
   // Frequency is stored in register 0x0e in bit 3 and 4
   Wire.beginTransmission(0x68);
   Wire.write(0x0e);
   Wire.endTransmission();
   Wire.requestFrom(0x68, 1);
   uint8_t register0E = Wire.read();

   // clear bits 3 and 4 for 1Hz
   register0E &= ~(1 << 3);
   register0E &= ~(1 << 4);

   // put the value of the register back
   Wire.beginTransmission(0x68);
   Wire.write(0x0e);
   Wire.write(register0E);
   Wire.endTransmission();
 }

Since I'm now qualified for low level programming, any suggestions on how to change the registers would be appreciated.