M41T93 Serial SPI bus real-time clock (RTC) with battery switchover Datasheet - production data Programmable 8-bit counter/timer 7 bytes of battery-backed user SRAM Battery low flag Low operating current of 80 A QFN16, 4 mm x 4 mm Oscillator stop detection Battery or supercapacitor backup 18 Operating temperature of 40 C to +85 C 1 Package options include a 16-lead QFN and an 18-lead embedded crystal SOIC SOX18, 11.61 x 7.62 mm (embedded crystal) Features Ultra-low battery supply current of 365 nA Factory calibrated accuracy 5 ppm typical after 2 reflows (SOX18) (much better accuracies are achievable using built-in programmable analog and digital calibration circuits) 2.0 V to 5.5 V clock operating voltage Counters for tenths/hundredths of seconds, seconds, minutes, hours, day, date, month, year, and century Automatic switchover and reset output circuitry (fixed reference): M41T93S: V = 3.0 V to 5.5 V CC M41T93R: V = 2.7 V to 5.5 V CC M41T93Z: V = 2.38 V to 5.50 V CC Compatible with SPI bus serial interface (supports SPI mode 0 CPOL = 0, CPHA = 0 ) Programmable alarm with interrupt function (valid even during battery backup mode) nd Optional 2 programmable alarm available Square wave output (defaults to 32 KHz on power-up) RESET (RST) output Watchdog timer November 2013 DocID12615 Rev 8 1/56 This is information on a product in full production. www.st.comContents M41T93 Contents 1 Description 6 1.1 SPI signal description 11 1.1.1 Serial data output (SDO) 11 1.1.2 Serial data input (SDI) 11 1.1.3 Serial clock (SCL) . 11 1.1.4 Chip enable (E) . 11 2 Operation . 12 2.1 SPI bus characteristics . 12 2.2 READ and WRITE cycles . 13 2.3 Data retention and battery switchover (V = V ) 15 SO RST 2.4 Power-on reset (t ) . 15 rec 3 Clock operation 16 3.1 Clock data coherency 17 3.1.1 Example of incoherency 17 3.1.2 Accessing the device . 18 3.2 Halt bit (HT) operation . 18 3.2.1 Power-down time stamp 19 3.3 Real-time clock accuracy . 21 3.4 Clock calibration 22 3.4.1 Digital calibration (periodic counter correction) . 22 3.4.2 Analog calibration (programmable load capacitance) 25 3.4.3 Pre-programmed calibration value . 26 3.5 Setting the alarm clock registers . 30 3.6 Optional second programmable alarm . 31 3.7 Watchdog timer 31 3.8 8-bit (countdown) timer . 32 3.8.1 Timer interrupt/output . 32 3.8.2 Timer flag (TF) 34 3.8.3 Timer interrupt enable (TIE) 34 3.8.4 Timer enable (TE) . 34 3.8.5 TD1/0 . 34 2/56 DocID12615 Rev 8