DS1904 RTC - How to Convert Binary Time into Real Time/Date?

[Ioannis]

Hi Bert.

The point that confussed me more was that the chip was not set by me. It was set by Maxim or another person far far away from me in a different time zone, before winter time.

As you can see by the attached picture above, it has 0-1 seconds difference from my PC! Amazing. There must be a trick.

I found this C program but could not understand what really does.

void loop(void) {
  byte i;
  byte present = 0;
  byte data[8];
  byte addr[8];
  uint32_t timestamp;
  int seconds = 0;

  if ( !ds.search(addr)) {
	//Serial.print("No more addresses found.\n");
	ds.reset_search();
	delay(500);  // for readability
	return;
  }

  present = ds.reset();
  ds.select(addr);
  ds.write(0x66,1);   // read RTC
  for ( i = 0; i < 5; i++) {
    data[i] = ds.read();
  }
	timestamp = data[1];
	timestamp = timestamp << 8;
	timestamp |= data[2];
	timestamp = timestamp << 8;
	timestamp |= data[3];
	timestamp = timestamp << 8;
	timestamp |= data[4];
Serial.println(timestamp);
delay(1000);
}

Ioannis

[cncmachineguy]

Hi Bert.

The point that confussed me more was that the chip was not set by me. It was set by Maxim or another person far far away from me in a different time zone, before winter time.

As you can see by the attached picture above, it has 0-1 seconds difference from my PC! Amazing. There must be a trick.

That is quite incredible! I dont get how the maxim reader could know when the timer was started

As for the code snippit, I don't know C, but it appears to just read the data into an array, and display it.

[Ioannis]

Yes it uses an array and does some oring and shifting.

I really have not quite understood the logic behind it.

A couple of days say Maxim for the AN to be approoved.

Will see...

Ioannis

[Ioannis]

Update from Maxim.

Well, finally the counter is pure binary and user have to set a referene time stamp.

So far OK. But how on earth can one calculate the date, months, leap years etc?

If anyone interested in the details of the AN from Maxim, PM. Code examples are in assembly though.

Ioannis