M41T00 Serial real-time clock Not For New Design Features For new designs use M41T00S Counters for seconds, minutes, hours, day, 8 month, years, and century 32 kHz crystal oscillator integrating load 1 capacitance (12.5 pF) providing exceptional oscillator stability and high crystal series resistance operation SO8(M) 2 Serial interface supports I C bus (100 kHz protocol) Ultra low battery supply current of 0.8 A (typ at 3 V) Description 2.0 to 5.5 V clock operating voltage The M41T00 is a low power serial real time clock Automatic switchover and deselect circuitry with a built-in 32.768 kHz oscillator (external (for 3 V application select M41T00S datasheet) crystal controlled). Eight bytes of the RAM are Software clock calibration to compensate used for the clock/calendar function and are crystal deviation due to temperature configured in binary coded decimal (BCD) format. Automatic leap year compensation Addresses and data are transferred serially via a two-line bidirectional bus. The built-in address Operating temperature of -40 to 85 C register is incremented automatically after each WRITE or READ data byte. The M41T00 clock has a built-in power sense circuit which detects power failures and automatically switches to the battery supply during power failures. The energy needed to sustain the RAM and clock operations can be supplied from a small lithium coin cell. Typical data retention time is in excess of 5 years with a 50 mA/h 3 V lithium cell (see Section 2.10: Data retention mode for AC/DC characteristics). The M41T00 is supplied in 8-lead plastic small outline package. May 2008 Rev 9 1/25 This is information on a product still in production but not recommended for new designs. www.st.com 1Contents M41T00 Contents 1 Device overview 5 2 Device operation 7 2.1 Wire bus characteristics . 7 2.2 Bus not busy 7 2.3 Start data transfer 7 2.4 Stop data transfer 8 2.5 Data valid 8 2.6 Acknowledge . 8 2.7 Characteristics . 10 2.8 READ mode . 10 2.9 WRITE mode 12 2.10 Data retention mode . 12 3 M41T00 clock operation . 14 3.1 Clock calibration 15 3.2 Output driver pin 17 3.3 Initial power-on defaults 17 4 Maximum ratings . 18 5 DC and AC parameters 19 6 Package mechanical data 21 7 Part numbering 23 8 Revision history . 24 2/25