M41T80 Serial access real-time clock with alarm Features Counters for tenths/hundredths of seconds, 8 seconds, minutes, hours, day, date, month, year, and century 1 32 KHz crystal oscillator integrating load capacitance (12.5 pF) providing exceptional oscillator stability and high crystal series SO8 resistance operation 8-pin SOIC 2 Serial interface supports I C bus (400 kHz) 2.0 to 5.5 V clock operating voltage 32 KHz square wave on power-up to drive a microcontroller in low-power mode Programmable (1 Hz to 32 KHz) square wave Programmable alarm and interrupt function Low operating current of 200 A Operating temperature of 40 to 85 C ECOPACK package available August 2011 Doc ID 9074 Rev 5 1/27 www.st.com 1Contents M41T80 Contents 1 Description . 5 2 Operation 7 2.1 2-Wire bus characteristics . 7 2.1.1 Bus not busy 7 2.1.2 Start data transfer 7 2.1.3 Stop data transfer 7 2.1.4 Data valid . 8 2.1.5 Acknowledge 8 2.2 READ mode . 10 2.3 WRITE mode 12 3 Clock operation 13 3.1 Clock registers . 13 3.2 Setting alarm clock registers 15 3.3 Full-time 32 KHz square wave output 16 3.4 Century bit 16 3.5 Output driver pin 17 3.6 Preferred power-on default 17 4 Maximum rating 18 5 DC and AC parameters 19 6 Package mechanical data 21 7 Part numbering 25 8 Revision history . 26 2/27 Doc ID 9074 Rev 5