DS3231M ±5ppm, I2C Real-Time Clock General Description The DS3231M is a low-cost, extremely accurate, I2C real-time clock (RTC). The device incorporates a battery input and maintains accurate timekeeping when main power to the device is interrupted. The integration of the microelectromechanical systems (MEMS) resonator enhances the long-term accuracy of the device and reduces the piece-part count in a manufacturing line. The DS3231M is available in the same footprint as the popular DS3231 RTC. The RTC maintains seconds, minutes, hours, day, date, month, and year information. The date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with an AM/PM indicator. Two programmable time-ofday alarms and a 1Hz output are provided. Address and data are transferred serially through an I2C bidirectional bus. A precision temperature-compensated voltage reference and comparator circuit monitors the status of VCC to detect power failures, to provide a reset output, and to automatically switch to the backup supply when necessary. Additionally, the RST pin is monitored as a pushbutton input for generating a microprocessor reset. See the Block Diagram for more details. Features STimekeeping Accuracy ±5ppm (±0.432 Second/ Day) from -45°C to +85°C SBattery Backup for Continuous Timekeeping SLow Power Consumption SFootprint and Functionally Compatible to DS3231 SComplete Clock Calendar Functionality Including Seconds, Minutes, Hours, Day, Date, Month, and Year with Leap Year Compensation Up to Year 2100 STwo Time-of-Day Alarms S1Hz and 32.768kHz Outputs SReset Output and Pushbutton Input with Debounce SFast (400kHz) I2C-Compatible Serial Bus S+2.3V to +5.5V Supply Voltage SDigital Temp Sensor with ±3°C Accuracy S-45°C to +85°C Temperature Range S8-Pin or 16-Pin SO Packages SUnderwriters Laboratories (UL) Recognized Typical Operating Circuit Applications Power Meters +3.3V +3.3V Industrial Applications Ordering Information PART TEMP RANGE PIN-PACKAGE DS3231MZ+ -45NC to +85NC 8 SO DS3231MZ/V+ -45NC to +85NC 8 SO DS3231M+ -45NC to +85NC 16 SO +Denotes a lead(Pb)-free/RoHS-compliant package. /V denotes an automotive qualified part. I/O PORT SCL SDA 32KHZ INTERRUPTS CPU VBAT INT/SQW RST DS3231M Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device may be simultaneously available through various sales channels. For information about device errata, go to: www.maximintegrated.com/errata. For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com. 19-5312; Rev 4; 9/12 DS3231M ±5ppm, I2C Real-Time Clock ABSOLUTE MAXIMUM RATINGS Voltage Range on Any Pin Relative to GND.........-0.3V to +6.0V Operating Temperature Range........................... -45NC to +85NC Storage Temperature Range............................. -55NC to +125NC Lead Temperature (soldering, 10s).................................+300NC Soldering Temperature (reflow).......................................+260NC Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. RECOMMENDED OPERATING CONDITIONS (TA = -45NC to +85NC, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS VCC 2.3 3.3 5.5 VBAT 2.3 3.0 5.5 Logic 1 VIH 0.7 x VCC VCC + 0.3 V Logic 0 VIL -0.3 0.3 x VCC V Supply Voltage V ELECTRICAL CHARACTERISTICS—FREQUENCY AND TIMEKEEPING (VCC or VBAT = +3.3V, TA = -45NC to +85NC, unless otherwise noted. Typical values are at VCC = +3.3V, VBAT = +3.0V, and TA = +25NC, unless otherwise noted.) PARAMETER 1Hz Frequency Tolerance SYMBOL Df/fOUT CONDITIONS MIN TYP Measured over R 10s interval MAX UNITS Q5 ppm 1Hz Frequency Stability vs. VCC Voltage Df/V Timekeeping Accuracy tKA Q0.432 Seconds/ Day Df/fOUT Q2.5 % 32kHz Frequency Tolerance ppm/V Q1 DC ELECTRICAL CHARACTERISTICS—GENERAL (VCC = +2.3V to +5.5V, TA = -45NC to +85NC, unless otherwise noted. Typical values are at VCC = +3.3V, VBAT = +3.0V, and TA = +25NC, unless otherwise noted.) PARAMETER SYMBOL Active Supply Current (I2C Active: Includes Temperature Conversion Current) ICCA Standby Supply Current (I2C Inactive: Includes Temperature Conversion Current) ICCS Temperature Conversion Current (I2C Inactive) ICCSCONV 2 CONDITIONS MIN TYP MAX VCC = +3.63V 200 VCC = VCCMAX 300 VCC = +3.63V 130 VCC = VCCMAX 200 VCC = +3.63V 575 VCC = VCCMAX 650 UNITS µA µA µA Maxim Integrated DS3231M ±5ppm, I2C Real-Time Clock DC ELECTRICAL CHARACTERISTICS—GENERAL (continued) (VCC = +2.3V to +5.5V, TA = -45NC to +85NC, unless otherwise noted. Typical values are at VCC = +3.3V, VBAT = +3.0V, and TA = +25NC, unless otherwise noted.) PARAMETER SYMBOL MIN TYP MAX UNITS 2.45 2.575 2.70 V IOL = 3mA 0.4 V IOL = 1mA 0.4 V -0.1 +0.1 µA ILI -0.1 +0.1 µA IOL -200 +10 µA 100 nA Power-Fail Voltage VPF Logic 0 Output (32KHZ, INT/SQW, SDA) VOL Logic 0 Output (RST) VOL Output Leakage (32KHZ, INT/SQW, SDA) ILO Input Leakage (SCL) RST I/O Leakage VBAT Leakage Temperature Accuracy CONDITIONS IBATLKG TEMPACC 25 VCC or VBAT = +3.3V Q3 NC Temperature Conversion Time tCONV 10 ms Pushbutton Debounce ms PBDB 250 Reset Active Time tRST 250 Oscillator Stop Flag (OSF) Delay tOSF (Note 2) 125 ms 200 ms DC ELECTRICAL CHARACTERISTICS—VBAT CURRENT CONSUMPTION (VCC = 0V, VBAT = +2.3V to +5.5V, TA = -45NC to +85NC, unless otherwise noted. Typical values are at VCC = 0V, VBAT = +3.0V, and TA = +25NC, unless otherwise noted.) PARAMETER SYMBOL Active Battery Current (I2C Active) (Note 3) IBATA Timekeeping Battery Current (I2C Inactive) (Note 3) IBATT Temperature Conversion Current (I2C Inactive) IBATTC Data Retention Current (Oscillator Stopped and I2C Inactive) IBATDR CONDITIONS MIN TYP MAX VBAT = +3.63V 70 VBAT = VBATMAX 150 VBAT = +3.63V, EN32KHZ = 0 2 3.0 VBAT = VBATMAX, EN32KHZ = 0 2 3.5 UNITS µA µA VBAT = +3.63V 575 VBAT = VBATMAX 650 TA = +25NC 100 nA MAX UNITS µA AC ELECTRICAL CHARACTERISTICS—POWER SWITCH (TA = -45NC to +85NC, unless otherwise noted.) (Figure 2) PARAMETER SYMBOL CONDITIONS MIN TYP VCC Fall Time, VPFMAX to VPFMIN tVCCF 300 Fs VCC Rise Time, VPFMIN to VPFMAX tVCCR 0 Fs Recovery at Power-Up Maxim Integrated tREC (Note 4) 250 300 ms 3 DS3231M ±5ppm, I2C Real-Time Clock AC ELECTRICAL CHARACTERISTICS—I2C INTERFACE (VCC or VBAT = +2.3V to +5.5V, TA = -45NC to +85NC, unless otherwise noted. Typical values are at VCC = +3.3V, VBAT = +3.0V, and TA = +25NC, unless otherwise noted.) (Note 5, Figure 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 400 kHz SCL Clock Frequency fSCL 0 Bus Free Time Between STOP and START Conditions tBUF 1.3 Fs Hold Time (Repeated) START Condition tHD:STA 0.6 Fs Low Period of SCL tLOW 1.3 Fs High Period of SCL tHIGH 0.6 Data Hold Time tHD:DAT 0 Data Set-Up Time tSU:DAT 100 ns START Set-Up Time tSU:STA 0.6 Fs SDA and SCL Rise Time tR (Note 6) 20 + 0.1CB 300 ns SDA and SCL Fall Time tF (Note 6) 20 + 0.1CB 300 ns STOP Set-Up Time SDA, SCL Input Capacitance tSU:STO CBIN Fs 0.9 0.6 (Note 7) Fs Fs 10 pF All voltages are referenced to ground. The parameter tOSF is the period of time the oscillator must be stopped for the OSF flag to be set. Includes the temperature conversion current (averaged). This delay applies only if the oscillator is enabled. If the EOSC bit is 1, tREC is bypassed and RST immediately goes high. The state of RST does not affect the I2C interface or RTC functions. Note 5: Interface timing shown is for fast-mode (400kHz) operation. This device is also backward-compatible with standard mode I2C timing. Note 6: CB: Total capacitance of one bus line in picofarads. Note 7: Guaranteed by design; not 100% production tested. Note Note Note Note 4 1: 2: 3: 4: Maxim Integrated DS3231M ±5ppm, I2C Real-Time Clock Timing Diagrams SDA tBUF tF tLOW tHD:STA tSP SCL tHD:STA tHIGH tR tHD:DAT STOP START tSU:STA tSU:STO tSU:DAT REPEATED START NOTE: TIMING IS REFERENCED TO VILMAX AND VIHMIN. Figure 1. I2C Timing tVCCF tVCCR VPFMAX VPFMIN VCC tREC RST Figure 2. Power Switch Timing RST PBDB tRST Figure 3. Pushbutton Reset Timing Maxim Integrated 5 DS3231M ±5ppm, I2C Real-Time Clock Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) VBAT = 2.3V, EN32KHZ = 1, IOUT = 0mA 140 +85°C 120 110 100 +25°C 90 -40°C 80 INCREASE BELOW VPF DUE TO INTERNAL PULLUP RESISTOR ON RST 70 60 VCC = 0V, EN32KHZ = 1, BBSQW = 0 3.5 SUPPLY CURRENT (µA) +85°C 3.0 +25°C 2.5 2.0 1.5 50 -40°C 1.0 2 3 4 5 6 2 3 SUPPLY VOLTAGE (V) 0.2 0.1 0.3 0.2 4 6 8 10 1 2 3 4 5 200 6 4 LIMITS 2 0 -2 -4 -6 -8 -10 0 50 TEMPERATURE (°C) 100 TA = +25°C 190 180 SUPPLY CURRENT (µA) FREQUENCY ERROR (ppm) 2 4 6 SUPPLY VOLTAGE (V) POWER-SUPPLY CURRENT vs. SCL FREQUENCY DS3231M toc06 VCC = 3.3V -50 0 OUTPUT CURRENT (mA) FREQUENCY ERROR vs. TEMPERATURE 8 TRACKS WITH VCC 2 0 0 OUTPUT CURRENT (mA) 10 3 DS3231M toc07 2 4 1 0 0 VBAT = 3.0V, TA = +25°C 5 0.1 0 6 6 OUTPUT VOLTAGE (V) 0.3 6 RST OUTPUT VOLTAGE vs. POWER SUPPLY VOLTAGE VCC = 2.45V, VBAT = 3.0V, TA = +25°C 0.4 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 0.4 0.5 DS3231M toc03 VCC = 2.3V, VBAT = 0V, TA = +25°C 5 RST OUTPUT VOLTAGE vs. OUTPUT CURRENT DS3231M toc04 INT/SQW OUTPUT VOLTAGE vs. OUTPUT CURRENT 0.5 4 SUPPLY VOLTAGE (V) DS3231M toc05 SUPPLY CURRENT (µA) 130 4.0 DS3231M toc01 150 BATTERY-SUPPLY CURRENT vs. BATTERY-SUPPLY VOLTAGE DS3231M toc02 POWER-SUPPLY CURRENT vs. POWER-SUPPLY VOLTAGE 170 +5.5V 160 150 140 130 120 +2.7V 110 100 90 80 +3.5V 0 100 200 300 400 SCL FREQUENCY (kHz) Maxim Integrated DS3231M ±5ppm, I2C Real-Time Clock Pin Configuration TOP VIEW 32KHZ 1 + 16 SCL VCC 2 INT/SQW 3 TOP VIEW 15 SDA DS3231M 14 VBAT 32KHZ 1 RST 4 13 GND VCC 2 N.C. 5 12 N.C. INT/SQW N.C. 6 11 N.C. RST N.C. 7 10 N.C. N.C. 8 9 + 8 SCL 7 SDA 3 6 VBAT 4 5 GND DS3231M SO N.C. SO Pin Description PIN NAME FUNCTION 8 SO 16 SO 1 1 32KHZ 32.768kHz Output (50% Duty Cycle). This open-drain pin requires an external pullup resistor. When enabled with the EN32KHZ bit in the Status register (0Fh), this output operates on either power supply. This pin can be left open circuit if not used. 2 2 VCC DC Power Pin for Primary Power Supply. This pin should be decoupled using a 0.1FF to 1.0FF capacitor. Connect to ground if not used. INT/ SQW Active-Low Interrupt or 1Hz Square-Wave Output. This open-drain pin requires an external pullup resistor connected to a supply at 5.5V or less. It can be left open if not used. This multifunction pin is determined by the state of the INTCN bit in the Control register (0Eh). When INTCN is set to logic 0, this pin outputs a 1Hz square wave. When INTCN is set to logic 1, a match between the timekeeping registers and either of the alarm registers activates the INT/SQW pin (if the alarm is enabled). Because the INTCN bit is set to logic 1 when power is first applied, the pin defaults to an interrupt output with alarms disabled. RST Active-Low Reset. This pin is an open-drain input/output. It indicates the status of VCC relative to the VPF specification. As VCC falls below VPF, the RST pin is driven low. When VCC exceeds VPF, for tRST, the RST pin is pulled high by the internal pullup resistor. The active-low, open-drain output is combined with a debounced pushbutton input function. This pin can be activated by a pushbutton reset request. It has an internal 50kI (RPU) nominal value pullup resistor to VCC. No external pullup resistors should be connected. If the oscillator is disabled, tREC is bypassed and RST immediately goes high. 3 3 4 4 — 5–12 N.C. No Connection. These pins must be connected to ground. 5 13 GND Ground VBAT Backup Power-Supply Input. When using the device with the VBAT input as the primary power source, this pin should be decoupled using a 0.1FF to 1.0FF low-leakage capacitor. When using the device with the VBAT input as the backup power source, the capacitor is not required. If VBAT is not used, connect to ground. The device is UL recognized to ensure against reverse charging when used with a primary lithium battery. Go to www.maximintegrated.com/qa/info/ul for more information. 6 14 Maxim Integrated 7 DS3231M ±5ppm, I2C Real-Time Clock Pin Description (continued) PIN NAME FUNCTION 15 SDA Serial-Data Input/Output. This pin is the data input/output for the I2C serial interface. This open-drain pin requires an external pullup resistor. The pullup voltage can be up to 5.5V, regardless of the voltage on VCC. 16 SCL Serial-Clock Input. This pin is the clock input for the I2C serial interface and is used to synchronize data movement on the serial interface. The pullup voltage can be up to 5.5V, regardless of the voltage on VCC. 8 SO 16 SO 7 8 Block Diagram 32KHZ DIVIDER DS3231M N INT/SQW 1Hz TIME-BASE RESONATOR VBAT VCC RPU POWER CONTROL INTERRUPT OR 1Hz SELECT N DIGITAL ADJUSTMENT RST TEMP SENSOR N FACTORY TRIM GND SDA SCL I2C INTERFACE CONTROL AND STATUS REGISTERS Detailed Description The DS3231M is a serial real-time clock (RTC) driven by an internal, temperature-compensated, microelectromechanical systems (MEMS) resonator. The oscillator provides a stable and accurate reference clock and maintains the RTC to within Q0.432 seconds-per-day accuracy from -45NC to +85NC. The RTC is a low-power clock/ calendar with two programmable time-of-day alarms. INT/ SQW provides either an interrupt signal due to alarm conditions or a 1Hz square wave. The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The date at the end of the month is automatically adjusted for months with fewer than 8 CLOCK/CALENDAR WITH ALARM 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with an AM/PM indicator. The internal registers are accessible though an I2C bus interface. A temperature-compensated voltage reference and comparator circuit monitors the level of VCC to detect power failures and to automatically switch to the backup supply when necessary. The RST pin provides an external pushbutton function and acts as an indicator of a power-fail event. Operation The Block Diagram shows the device’s main elements. Each of the major blocks is described separately in the following sections. Maxim Integrated DS3231M ±5ppm, I2C Real-Time Clock High-Accuracy Time Base +3.3V The temperature sensor, oscillator, and digital adjustment controller logic form the highly accurate time base. The controller reads the output of the on-board temperature sensor and adjusts the final 1Hz output to maintain the required accuracy. The device is trimmed at the factory to maintain a tight accuracy over the operating temperature range. When the device is powered by VCC, the adjustment occurs once a second. When the device is powered by VBAT, the adjustment occurs once every 10s to conserve power. Adjusting the 1Hz time base less often does not affect the device’s long-term timekeeping accuracy. The device also contains an Aging Offset register that allows a constant offset (positive or negative) to be added to the factory-trimmed adjustment value. VCC VBAT Figure 4. Single Supply (VCC Only) VCC Power-Supply Configurations The DS3231M can be configured to operate on a single power supply (using either VCC or VBAT) or in a dualsupply configuration, which provides a backup supply source to keep the timekeeping circuits alive during absence of primary system power. VBAT Figure 4 illustrates a single-supply configuration using VCC only, with the VBAT input grounded. When VCC < VPF, the RST output is asserted (active low). Temperature conversions are executed once per second. Figure 5. Single Supply (VBAT Only) Figure 5 illustrates a single-supply configuration using VBAT only, with the VCC input grounded. The RST output is disabled and is held at ground through the connection of the internal pullup resistor. Temperature conversions are executed once every 10s. +3.3V VCC Figure 6 illustrates a dual-supply configuration, using the VCC supply for normal system operation and the VBAT supply for backup power. In this configuration, the power-selection function is provided by a temperaturecompensated voltage reference and a comparator circuit that monitors the VCC level. When VCC is greater than VPF, the device is powered by VCC. When VCC is less than VPF but greater than VBAT, the device is powered VBAT Figure 6. Dual Power Supply Table 1. Power Control CONFIGURATION CONDITION VCC Only (Figure 4) VCC > VPF VBAT Only (Figure 5) EOSC = 0 Dual Supply (Figure 6) Maxim Integrated VCC < VPF EOSC = 1 VCC > VPF VCC < VPF I/O ACTIVE I/O INACTIVE ICCA ICCS Active (Low) IBATT IBATA Disabled (Low) IBATDR ICCA RST Inactive (High) ICCS Inactive (High) VCC > VBAT ICCA VCC > VBAT ICCS VCC < VBAT IBATA VCC < VBAT IBATT Active (Low) 9 DS3231M ±5ppm, I2C Real-Time Clock by VCC. If VCC is less than VPF and is less than VBAT, the device is powered by VBAT (see Table 1). When VCC < VPF, the RST output is asserted (active low). When VCC is the presently selected power source, temperature conversions are executed once per second. When VBAT is the presently selected power source, temperature conversions are executed once every 10s. To preserve the battery, the first time VBAT is applied to the device the oscillator does not start up until VCC exceeds VPF or until a valid I2C address is written to the device. Typical oscillator startup time is less than 1s. Approximately 2s after VCC is applied, or a valid I2C address is written, the device makes a temperature measurement and applies the calculated correction to the oscillator. Once the oscillator is running, it continues to run as long as a valid power source is available (VCC or VBAT), and the device continues to measure the temperature and correct the oscillator frequency. On the first application of VCC power, or (if VBAT powered) when a valid I2C address is written to the device, the time and date registers are reset to 01/01/00 01 00:00:00 (DD/MM/ YY DOW HH:MM:SS). VBAT Operation There are several modes of operation that affect the amount of VBAT current that is drawn. While the device is powered by VBAT and the serial interface is active, the active battery current IBATA is drawn. When the serial interface is inactive, the timekeeping current IBATT (which includes the averaged temperature-conversion current IBATTC) is used. The temperature-conversion current IBATTC is specified since the system must be able to support the periodic higher current pulse and still maintain a valid voltage level. The data-retention current IBATDR is the current drawn by the device when the oscillator is stopped (EOSC = 1). This mode can be used to minimize battery requirements for periods when maintaining time and date information is not necessary, e.g., while the end system is waiting to be shipped to a customer. Pushbutton Reset Function The device provides for a pushbutton switch to be connected to the RST input/output pin. When the device is not in a reset cycle, it continuously monitors RST for a low-going edge. If an edge transition is detected, the device debounces the switch by pulling RST low. After the internal timer has expired (PBDB), the device continues to monitor the RST line. If the line is still low, the device continuously monitors the line looking for a rising 10 edge. Upon detecting release, the device forces RST low and holds it low for tRST. RST is also used to indicate a power-fail condition. When VCC is lower than VPF, an internal power-fail signal is generated, which forces RST low. When VCC returns to a level above VPF, RST is held low for approximately 250ms (tREC) to allow the power supply to stabilize. If the oscillator is not running when VCC is applied, tREC is bypassed and RST immediately goes high. Assertion of the RST output, whether by pushbutton or power-fail detection, does not affect the device’s internal operation. RST output operation and pushbutton monitoring are only available if VCC power is available. Real-Time Clock (RTC) With the 1Hz source from the temperature-compensated oscillator, the RTC provides seconds, minutes, hours, day, date, month, and year information. The date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or the 12-hour format with an AM/PM indicator. The clock provides two programmable time-of-day alarms. INT/SQW can be enabled to generate either an interrupt due to an alarm condition or a 1Hz square wave. This selection is controlled by the INTCN bit in the Control register. I2C Interface The I2C interface is accessible whenever either VCC or VBAT is at a valid level. If a microcontroller connected to the device resets because of a loss of VCC or other event, it is possible that the microcontroller and device’s I2C communications could become unsynchronized, e.g., the microcontroller resets while reading data from the device. When the microcontroller resets, the device’s I2C interface can be placed into a known state by toggling SCL until SDA is observed to be at a high level. At that point the microcontroller should pull SDA low while SCL is high, generating a START condition. Address Map Table 2 shows the address map for the device’s timekeeping registers. During a multibyte access, when the address pointer reaches the end of the register space (12h), it wraps around to location 00h. On an I2C START or address pointer incrementing to location 00h, the current time is transferred to a second set of registers. The time information is read from these secondary registers, while the clock can continue to run. This eliminates the need to reread the registers in case the main registers update during a read. Maxim Integrated DS3231M ±5ppm, I2C Real-Time Clock Table 2. Timekeeping Registers ADDRESS BIT 7 MSB 00h 0 10 Seconds 01h 0 10 Minutes 02h 0 12/24 20 Hours 03h 0 0 0 04h 0 0 05h Century 0 BIT 6 BIT 5 AM/PM 06h BIT 4 BIT 3 BIT 2 0 RANGE Seconds Seconds 00–59 Minutes Minutes 00–59 Hour Hours 1–12 + AM/PM 00–23 0 Day 1–7 Date Day Date 01–31 Month Month/Century 01–12 + Century Year Year 00–99 10 Date 10 Month 0 BIT 0 LSB FUNCTION 10 Hours BIT 1 10 Year 07h A1M1 10 Seconds Seconds Alarm 1 Seconds 00–59 08h A1M2 10 Minutes Minutes Alarm 1 Minutes 00–59 Hour Alarm 1 Hours 1–12 + AM/PM 00–23 AM/PM 10 Hours 09h A1M3 12/24 0Ah A1M4 DY/DT 0Bh A2M2 0Ch A2M3 12/24 0Dh A2M4 DY/DT 0Eh EOSC OSF BBSQW CONV NA NA INTCN A2IE 0Fh 0 0 0 EN32KHZ BSY A2F 10h SIGN DATA DATA DATA DATA DATA DATA 20 Hours Day Alarm 1 Day 1–7 Date Alarm 1 Date 1–31 Minutes Alarm 2 Minutes 00–59 Hour Alarm 2 Hours 1–12 + AM/PM 00–23 10 Date 10 Minutes AM/PM 20 Hours 10 Hours 10 Date Day Alarm 2 Day 1–7 Date Alarm 2 Date 1–31 A1IE Control — A1F Status — DATA Aging Offset 81h–7Fh — — 11h SIGN DATA DATA DATA DATA DATA DATA DATA Temperature MSB 12h DATA DATA 0 0 0 0 0 0 Temperature LSB Note: Unless otherwise specified, the registers’ state is not defined when power is first applied. Clock and Calendar The time and calendar information is obtained by reading the appropriate register bytes. Table 2 shows the RTC registers. The time and calendar data are set or initialized by writing the appropriate register bytes. The contents of the time and calendar registers are in the binary-coded decimal (BCD) format. The device can Maxim Integrated be run in either 12-hour or 24-hour mode. Bit 6 of the Hours register is defined as the 12-hour or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour mode, bit 5 is the AM/PM bit with logic-high being PM. In the 24-hour mode, bit 5 is the 20-hour bit (20–23 hours). The century bit (bit 7 of the Month register) is toggled when the Years register overflows from 99 11 DS3231M ±5ppm, I2C Real-Time Clock to 00. The day-of-week register increments at midnight. Values that correspond to the day of week are userdefined but must be sequential (i.e., if 1 equals Sunday, then 2 equals Monday, and so on). Illogical time and date entries result in undefined operation. When reading or writing the time and date registers, secondary buffers are used to prevent errors when the internal registers update. When reading the time and date registers, the secondary buffers are synchronized to the internal registers on any I2C START and when the register pointer rolls over to zero. The time information is read from these secondary registers, while the clock continues to run. This eliminates the need to reread the registers in case the main registers update during a read. The countdown chain is reset whenever the seconds register is written. Write transfers occur on the acknowledge from the device. Once the countdown chain is reset, to avoid rollover issues the remaining time and date registers must be written within 1s. Alarms The device contains two time-of-day/date alarms. Alarm 1 can be set by writing to registers 07h–0Ah. Alarm 2 can be set by writing to registers 0Bh–0Dh. See Table 2. The alarms can be programmed (by the alarm enable and INTCN bits in the Control register) to activate the INT/SQW output on an alarm match condition. Bit 7 of each of the time-of-day/date alarm registers are mask bits (Table 2). When all the mask bits for each alarm are logic 0, an alarm only occurs when the values in the timekeeping registers match the corresponding values stored in the time-of-day/date alarm registers. The alarms can also be programmed to repeat every second, minute, hour, day, or date. Table 3 shows the possible settings. Configurations not listed in the table result in illogical operation. The DY/DT bits (bit 6 of the alarm day/date registers) control whether the alarm value stored in bits 0–5 of that register reflects the day of the week or the date of the month. If DY/DT is written to logic 0, the alarm is the result of a match with date of the month. If DY/DT is written to logic 1, the alarm is the result of a match with day of the week. When the RTC register values match alarm register settings, the corresponding alarm flag A1F or A2F bit is set to logic 1. If the corresponding alarm interrupt enable A1IE or A2IE bit is also set to logic 1, the alarm condition activates the INT/SQW signal if the INTCN bit is set to logic 1. The match is tested on the once-per-second update of the time and date registers. Table 3. Alarm Mask Bits DY/DT ALARM RATE A1M3 A1M2 A1M1 X 1 1 1 1 Alarm once a second X 1 1 1 0 Alarm when seconds match X 1 1 0 0 Alarm when minutes and seconds match X 1 0 0 0 Alarm when hours, minutes, and seconds match 0 0 0 0 0 Alarm when date, hours, minutes, and seconds match 1 0 0 0 0 Alarm when day, hours, minutes, and seconds match DY/DT 12 ALARM 1 REGISTER MASK BITS (BIT 7) A1M4 ALARM 2 REGISTER MASK BITS (BIT 7) ALARM RATE A2M4 A2M3 A2M2 X 1 1 1 Alarm once per minute (00 seconds of every minute) X 1 1 0 Alarm when minutes match X 1 0 0 Alarm when hours and minutes match 0 0 0 0 Alarm when date, hours, and minutes match 1 0 0 0 Alarm when day, hours, and minutes match Maxim Integrated DS3231M ±5ppm, I2C Real-Time Clock Control Register (0Eh) BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 EOSC 0 BBSQW CONV NA NA INTCN A2IE A1IE 0 0 1 1 1 0 0 BIT 7 EOSC: Enable oscillator. When set to logic 0, the oscillator is started. When set to logic 1, the oscillator is stopped when the device switches to VBAT. This bit is clear (logic 0) when power is first applied. When the device is powered by VCC, the oscillator is always on regardless of the status of the EOSC bit. When the oscillator is disabled, all register data is static. BIT 6 BBSQW: Battery-backed square-wave enable. When set to logic 1 with INTCN = 0 and VCC < VPF, this bit enables the 1Hz square wave. When BBSQW is logic 0, INT/SQW goes high impedance when VCC falls below VPF. This bit is disabled (logic 0) when power is first applied. BIT 5 CONV: Convert temperature. Setting this bit to 1 forces the temperature sensor to convert the temperature into digital code and execute the temperature compensate algorithm to update the oscillator’s accuracy. The device cannot be forced to execute the temperature-compensate algorithm faster than once per second. A user-initiated temperature conversion does not affect the internal update cycle. The CONV bit remains at a 1 from the time it is written until the temperature conversion is completed, at which time both CONV and BSY go to 0. The CONV bit should be used when monitoring the status of a user-initiated conversion. See Figure 7 for more details. BITS 4:3 NA: Not applicable. These bits have no affect on the device and can be set to either 0 or 1. BIT 2 INTCN: Interrupt control. This bit controls the INT/SQW output signal. When the INTCN bit is set to logic 0, a 1Hz square wave is output on INT/SQW. When the INTCN bit is set to logic 1, a match between the timekeeping registers and either of the alarm registers activates the INT/SQW output (if the alarm is also enabled). The corresponding alarm flag is always set regardless of the state of the INTCN bit. The INTCN bit is set to a logic 1 when power is first applied. BIT 1 A2IE: Alarm 2 interrupt enable. When set to logic 1, this bit permits the alarm 2 flag (A2F) bit in the status register to assert INT/SQW (when INTCN = 1). When the A2IE bit is set to logic 0 or INTCN is set to logic 0, the A2F bit does not initiate an interrupt signal. The A2IE bit is disabled (logic 0) when power is first applied. BIT 0 A1IE: Alarm 1 interrupt enable. When set to logic 1, this bit permits the alarm 1 flag (A1F) bit in the status register to assert INT/SQW (when INTCN = 1). When the A1IE bit is set to logic 0 or INTCN is set to logic 0, the A1F bit does not initiate an interrupt signal. The A1IE bit is disabled (logic 0) when power is first applied. Maxim Integrated 13 DS3231M ±5ppm, I2C Real-Time Clock VCC POWERED INTERNAL 1Hz CLOCK BSY CONV THE USER SETS THE CONV BIT THE DEVICE CLEARS THE CONV BIT AFTER THE TEMPERATURE CONVERSION HAS COMPLETED BSY IS HIGH DURING THE TEMPERATURE CONVERSION VBAT POWERED 10 SECONDS INTERNAL 1Hz CLOCK BSY CONV THE USER SETS THE CONV BIT THE DEVICE CLEARS THE CONV BIT AFTER THE TEMPERATURE CONVERSION HAS COMPLETED Figure 7. CONV Control Bit and BSY Status Bit Operation 14 Maxim Integrated DS3231M ±5ppm, I2C Real-Time Clock Status Register (0Fh) BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 OSF 0 0 0 EN32KHZ BSY A2F A1F 1 0 0 0 1 X X X OSF: Oscillator stop flag. A logic 1 in this bit indicates that the oscillator either is stopped or was stopped for some period and could be used to judge the validity of the timekeeping data. This bit is set to logic 1 any time that the oscillator stops. This bit remains at logic 1 until written to logic 0. The following are examples of BIT 7 BITS 6:4 conditions that can cause the OSF bit to be set: 1) The first time power is applied. 2) The voltages present on both VCC and VBAT are insufficient to support the oscillator. 3) The EOSC bit is turned off in battery-backed mode. 4) External influences on the oscillator (i.e., noise, leakage, etc.). Unused (0). These bits have no meaning and are fixed at 0 when read. BIT 3 EN32KHZ: Enabled 32.768kHz output. This bit enables and disables the 32KHZ output. When set to a logic 0, the 32KHZ output is high impedance. On initial power-up, this bit is set to a logic 1 and the 32KHZ output is enabled and produces a 32.768kHz square wave if the oscillator is enabled. BIT 2 BSY: Busy. This bit indicates the device is busy executing temperature conversion function. It goes to logic 1 when the conversion signal to the temperature sensor is asserted, and then it is cleared when the device has completed the temperature conversion. See the Block Diagram for more details. BIT 1 A2F: Alarm 2 flag. A logic 1 in the alarm 2 flag bit indicates that the time matched the alarm 2 registers. If the A2IE bit is logic 1 and the INTCN bit is set to logic 1, INT/SQW is also asserted. A2F is cleared when written to logic 0. This bit can only be written to logic 0. Attempting to write to logic 1 leaves the value unchanged. BIT 0 A1F: Alarm 1 flag. A logic 1 in the alarm 1 flag bit indicates that the time matched the alarm 1 registers. If the A1IE bit is logic 1 and the INTCN bit is set to logic 1, INT/SQW is also asserted. A1F is cleared when written to logic 0. This bit can only be written to logic 0. Attempting to write to logic 1 leaves the value unchanged. Aging Offset Register (10h) BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 SIGN DATA DATA DATA DATA DATA DATA DATA 0 0 0 0 0 0 0 0 The Aging Offset register takes a user-provided value to add to or subtract from the factory-trimmed value that adjusts the accuracy of the time base. Use of the Aging Offset register is not needed to achieve the accuracy as defined in the Electrical Characteristics tables. The Aging Offset code is encoded in two’s complement, with bit 7 representing the SIGN bit and a valid range of ±127. One LSB typically represents a 0.12ppm change in frequency. The change in ppm per LSB is the same over the operating temperature range. Positive offsets slow the time base and negative offsets quicken the time base. Maxim Integrated 15 DS3231M ±5ppm, I2C Real-Time Clock Temperature Registers (11h-12h) Temperature Register (Upper Byte = 11h) BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 SIGN DATA DATA DATA DATA DATA DATA DATA 0 0 0 0 0 0 0 0 Temperature Register (Lower Byte = 12h) BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 DATA DATA 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Temperature is represented as a 10-bit code with a resolution of 0.25°C and is accessible at location 11h and 12h. The temperature is encoded in two’s complement format. The upper 8 bits, the integer portion, are at location 11h and the lower 2 bits, the fractional portion, are at location 12h. For example, 00011001 01b = +25.25°C. Upon power reset, the registers are set to a default temperature of 0°C and the controller starts a temperature conversion. The temperature is read upon initial application of VCC or I2C access on VBAT and once every second afterwards with VCC power or once every 10s with VBAT power. The Temperature registers are also updated after each user-initiated conversion and are read only. I2C Serial Port Operation I2C Slave Address The device’s slave address byte is D0h. The first byte sent to the device includes the device identifier, device address, and the R/W bit (Figure 8). The device address sent by the I2C master must match the address assigned to the device. I2C Definitions The following terminology is commonly used to describe I2C data transfers. Master Device: The master device controls the slave devices on the bus. The master device generates SCL clock pulses and START and STOP conditions. Slave Devices: Slave devices send and receive data at the master’s request. LSB MSB 1 1 0 1 DEVICE IDENTIFIER 0 0 0 R/W READ/ WRITE BIT Bus Idle or Not Busy: Time between STOP and START conditions when both SDA and SCL are inactive and in their logic-high states. When the bus is idle, it often initiates a low-power mode for slave devices. START Condition: A START condition is generated by the master to initiate a new data transfer with a slave. Transitioning SDA from high to low while SCL remains high generates a START condition. See Figure 1 for applicable timing. STOP Condition: A STOP condition is generated by the master to end a data transfer with a slave. Transitioning SDA from low to high while SCL remains high generates a STOP condition. See Figure 1 for applicable timing. Repeated START Condition: The master can use a repeated START condition at the end of one data transfer to indicate that it immediately initiates a new data transfer following the current one. Repeated STARTs are commonly used during read operations to identify a specific memory address to begin a data transfer. A repeated START condition is issued identically to a normal START condition. See Figure 1 for applicable timing. Figure 8. I2C Slave Address Byte 16 Maxim Integrated DS3231M ±5ppm, I2C Real-Time Clock Bit Write: Transitions of SDA must occur during the low state of SCL. The data on SDA must remain valid and unchanged during the entire high pulse of SCL plus the setup and hold time requirements (see Figure 1). Data is shifted into the device during the rising edge of the SCL. Bit Read: At the end of a write operation, the master must release the SDA bus line for the proper amount of setup time (see Figure 1) before the next rising edge of SCL during a bit read. The device shifts out each bit of data on SDA at the falling edge of the previous SCL pulse and the data bit is valid at the rising edge of the current SCL pulse. Remember that the master generates all SCL clock pulses including when it is reading bits from the slave. Acknowledge (ACK and NACK): An acknowledge (ACK) or not acknowledge (NACK) is always the ninth bit transmitted during a byte transfer. The device receiving data (the master during a read or the slave during a write operation) performs an ACK by transmitting a 0 during the ninth bit. A device performs a NACK by transmitting a 1 during the ninth bit. Timing for the ACK and NACK is identical to all other bit writes. An ACK is the acknowledgment that the device is properly receiving data. A NACK is used to terminate a read sequence or as an indication that the device is not receiving data. Byte Write: A byte write consists of 8 bits of information transferred from the master to the slave (most significant bit first) plus a 1-bit acknowledgment from the slave to the master. The 8 bits transmitted by the master are done according to the bit write definition and the acknowledgment is read using the bit read definition. Byte Read: A byte read is an 8-bit information transfer from the slave to the master plus a 1-bit ACK or NACK from the master to the slave. The 8 bits of information that are transferred (most significant bit first) from the slave to the master are read by the master using the bit read definition, and the master transmits an ACK using the bit write definition to receive additional data bytes. The master must NACK the last byte read to terminate communication so the slave returns control of SDA to the master. Slave Address Byte: Each slave on the I2C bus responds to a slave address byte sent immediately following a START condition. The slave address byte contains the slave address in the most significant 7 Maxim Integrated bits and the R/W bit in the least significant bit. The device’s slave address is D0h and cannot be modified by the user. When the R/W bit is 0 (such as in D0h), the master is indicating it writes data to the slave. If R/W = 1 (D1h in this case), the master is indicating it wants to read from the slave. If an incorrect slave address is written, the device assumes the master is communicating with another I2C device and ignore the communication until the next START condition is sent. Memory Address: During an I2C write operation, the master must transmit a memory address to identify the memory location where the slave is to store the data. The memory address is always the second byte transmitted during a write operation following the slave address byte. I2C Communication See Figure 9 for an I2C communication example. Writing a Single Byte to a Slave: The master must generate a START condition, write the slave address byte (R/W = 0), write the memory address, write the byte of data, and generate a STOP condition. Remember the master must read the slave’s acknowledgment during all byte write operations. Writing Multiple Bytes to a Slave: To write multiple bytes to a slave, the master generates a START condition, writes the slave address byte (R/W = 0), writes the starting memory address, writes multiple data bytes, and generates a STOP condition. Reading a Single Byte from a Slave: Unlike the write operation that uses the specified memory address byte to define where the data is to be written, the read operation occurs at the present value of the memory address counter. To read a single byte from the slave, the master generates a START condition, writes the slave address byte with R/W = 1, reads the data byte with a NACK to indicate the end of the transfer, and generates a STOP condition. However, since requiring the master to keep track of the memory address counter is impractical, use the method for manipulating the address counter for reads. Manipulating the Address Counter for Reads: A dummy write cycle can be used to force the address counter to a particular value. To do this the master generates a START condition, writes the slave address byte (R/W = 0), writes the memory address where it desires to read, generates a repeated START condition, writes the slave address byte (R/W = 1), 17 DS3231M ±5ppm, I2C Real-Time Clock TYPICAL I2C WRITE TRANSACTION MSB START 1 LSB 1 0 1 0 0 0 R/W MSB SLAVE ACK b7 LSB b6 READ/ WRITE SLAVE ADDRESS b5 b4 b3 b2 b1 b0 MSB SLAVE ACK b7 LSB b6 b5 b4 REGISTER ADDRESS b3 b2 b1 b0 SLAVE ACK STOP DATA EXAMPLE I2C TRANSACTIONS D0h A) SINGLE BYTE WRITE -WRITE CONTROL REGISTER TO 44h START 11010000 D0h B) SINGLE BYTE READ -READ CONTROL REGISTER START 1 1 0 1 0 0 0 0 0Eh SLAVE 00001110 ACK 0Eh SLAVE SLAVE 00001110 ACK ACK D0h C) MULTIBYTE WRITE -WRITE DATE REGISTER TO "02" AND MONTH REGISTER TO "11" D) MULTIBYTE READ -READ ALARM 2 HOURS AND DATE VALUES START 1 1 0 1 0 0 0 0 04h SLAVE ACK 00000100 SLAVE ACK 00001100 D0h START 1 1 0 1 0 0 0 0 44h SLAVE 01000100 ACK SLAVE ACK STOP D1h REPEATED START DATA 11010001 00000010 SLAVE ACK REPEATED START SLAVE ACK 00010001 SLAVE ACK SLAVE ACK VALUE D1h 0Ch VALUE MASTER NACK STOP 11h 02h SLAVE ACK SLAVE ACK 11010001 STOP DATA DATA MASTER ACK VALUE MASTER NACK STOP Figure 9. I2C Transactions reads data with ACK or NACK as applicable, and generates a STOP condition. See Figure 6 for a read example using the repeated START condition to specify the starting memory location. Reading Multiple Bytes from a Slave: The read operation can be used to read multiple bytes with a single transfer. When reading bytes from the slave, the master simply ACKs the data byte if it desires to read another byte before terminating the transaction. After the master reads the last byte it must NACK to indicate the end of the transfer and then it generates a STOP condition. Applications Information Power-Supply Decoupling To achieve the best results when using the DS3231M, decouple the VCC and/or VBAT power supplies with 0.1FF and/or 1.0FF capacitors. Use a high-quality, ceramic, surface-mount capacitor if possible. Surfacemount components minimize lead inductance, which improves performance, and ceramic capacitors tend to have adequate high-frequency response for decoupling applications. 18 If communications during battery operation are not required, the VBAT decoupling capacitor can be omitted. Using Open-Drain Outputs The 32KHZ and INT/SQW outputs are open drain and therefore require external pullup resistors to realize logichigh output levels. Pullup resistor values between 1kI and 10MI are typical. The RST output is also open drain, but is provided with an internal 50kI pullup resistor (RPU) to VCC. External pullup resistors should not be added. SDA and SCL Pullup Resistors SDA is an open-drain output and requires an external pullup resistor to realize a logic-high level. Because the device does not use clock cycle stretching, a master using either an open-drain output with a pullup resistor or CMOS output driver (push-pull) could be used for SCL. Battery Charge Protection The device contains Maxim Integrated’s redundant battery-charge protection circuit to prevent any charging of the external battery. Maxim Integrated DS3231M ±5ppm, I2C Real-Time Clock Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 16 SO W16MK+1 21-0042 90-0107 8 SO S8MK+1 21-0041 90-0096 Maxim Integrated 19 DS3231M ±5ppm, I2C Real-Time Clock Revision History REVISION NUMBER REVISION DATE 0 6/10 Initial release 5/11 Updated the Features section; moved the temperature accuracy limit from ±3°C (max) to ±3°C (typ) in the DC Electrical Characteristics—General table; added the PowerSupply Current vs. SCL Frequency graph to the Typical Operating Characteristics section; changed the initial date information to international format in the Power-Supply Configuration section 1, 3, 6, 10 2 10/11 Removed future status from the 8-pin SO package in the Ordering Information table; updated the Typical Operating Circuit; added Note 7 to the CBIN parameter in the AC Electrical Characteristics—I2C Interface table; clarified the 10h register range in Table 2 and the Aging Offset Register (10h) section; corrected the package codes for both SO variants in the Package Information table 1, 4, 11, 15, 19 3 12/11 Added the automotive qualified 8-pin SO package to the Ordering Information table; changed the lead temperature from +260°C to +300°C in the Absolute Maximum Ratings section 4 9/12 Changed the operating temperature range from -40°C to +85°C to -45°C to +85°C 1 DESCRIPTION PAGES CHANGED — 1, 2 1-4, 8 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. 20 © 2012 Maxim Integrated Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.