DS1338 I C RTC with 56-Byte NV RAM 2 www.maxim-ic.com GENERAL DESCRIPTION FEATURES The DS1338 serial real-time clock (RTC) is a lowpower, full binary-coded decimal (BCD) clock/calendar plus 56 bytes of NV SRAM. Address and data are transferred serially through an I2C interface. The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The end of the month date 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 AM/PM indicator. The DS1338 has a built-in powersense circuit that detects power failures and automatically switches to the backup supply, maintaining time and date operation APPLICATIONS ORDERING INFORMATION Handhelds (GPS, POS Terminal) Consumer Electronics (Set-Top Box, Digital Recording, Network Appliance) Office Equipment (Fax/Printer, Copier) Medical (Glucometer, Medicine Dispenser) Telecommunications (Router, Switcher, Server) Other (Utility Meter, Vending Machine, Thermostat, Modem) TYPICAL OPERATING CIRCUIT RPU = tr/Cb VCC VCC CRYSTAL VCC RPU RTC Counts Seconds, Minutes, Hours, Date of the Month, Month, Day of the Week, and Year with Leap-Year Compensation Valid Up to 2100 Available in a Surface-Mount Package with an Integrated Crystal (DS1338C) 56-Byte Battery-Backed NV RAM for Data Storage I2C Serial Interface Programmable Square-Wave Output Signal Automatic Power-Fail Detect and Switch Circuitry -40°C to +85°C Operating Temperature Range Underwriters Laboratory (UL) Recognized RPU X1 SCL CPU X2 VCC SQW/OUT DS1338 SDA GND i VBAT Pin Configurations appear at end of data sheet. 1 of 16 PART TEMP RANGE PIN-PACKAGE TOP MARK† DS1338Z-18 DS1338Z-18+ DS1338Z-3 DS1338Z-3+ DS1338Z-33 DS1338Z-33+ -40°C to +85°C -40°C to +85°C -40°C to +85°C -40°C to +85°C -40°C to +85°C -40°C to +85°C 8 SO (0.150″) 8 SO (0.150″) 8 SO (0.150″) 8 SO (0.150″) 8 SO (0.150″) 8 SO (0.150″) DS1338U-18 -40°C to +85°C 8 µSOP DS1338U-18+ -40°C to +85°C 8 µSOP DS1338U-3 -40°C to +85°C 8 µSOP DS1338U-3+ -40°C to +85°C 8 µSOP DS1338U-33 -40°C to +85°C 8 µSOP DS1338U-33+ -40°C to +85°C 8 µSOP DS1338-18 DS1338-18 DS1338-3 DS1338-3 DS133833 DS133833 1338 rr-18 1338 rr-18 1338 rr-3 1338 rr-3 1338 rr-33 1338 rr-33 DS1338C-18 DS1338C-18 DS1338C-3 DS1338C-3 DS1338C-33 DS1338C-33 DS1338C-18 -40°C to +85°C 16 SO (0.300″) DS1338C-18# -40°C to +85°C 16 SO (0.300″) DS1338C-3 -40°C to +85°C 16 SO (0.300″) DS1338C-3# -40°C to +85°C 16 SO (0.300″) DS1338C-33 -40°C to +85°C 16 SO (0.300″) DS1338C-33# -40°C to +85°C 16 SO (0.300″) rr = second line, revision level + Denotes a lead-free/RoHS-compliant device. # Denotes a RoHS-compliant device that may include lead that is exempt under the RoHS requirements. The lead finish is JESD97 category e3, and is compatible with both lead-based and lead-free soldering processes. † A “+” anywhere on the top mark denotes a lead-free device. A “#” denotes a RoHS-compliant device. REV: 010307 DS1338 I2C RTC with 56-Byte NV RAM ABSOLUTE MAXIMUM RATINGS Voltage Range on Any Pin Relative to Ground………………………………………………………..……..-0.3V to +6.0V Operating Temperature Range…………………………………………………………………………..……-40°C to +85°C Storage Temperature Range………………………………………………………………………………...-55°C to +125°C Soldering Temperature…………….....See precautions in the Handling, PC Board Layout, and Assembly Section. 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 the absolute maximum rating conditions for extended periods may affect device reliability. RECOMMENDED DC OPERATING CONDITIONS (VCC = VCC(MIN) to VCC(MAX), TA = -40°C to +85°C, unless otherwise noted. Typical values are at VCC = 3.3V, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS Supply Voltage VCC DS1338-18 DS1338-3 DS1338-33 Logic 1 VIH (Note 2) Logic 0 VIL (Note 2) Pullup Resistor Voltage (SQW/OUT) VPU (Note 2) Power-Fail Voltage VPF VBAT Input Voltage VBAT MIN TYP MAX 1.71 2.7 3.0 0.7 x VCC 1.8 3.0 3.3 1.89 3.3 5.5 VCC + 0.3 +0.3 x VCC -0.3 5.5 DS1338-18 DS1338-3 DS1338-33 (Note 2) 1.51 2.45 2.70 1.3 1.62 2.59 2.82 3.0 1.71 2.70 2.97 3.7 UNITS V V V V V V DC ELECTRICAL CHARACTERISTICS (VCC = VCC(MIN) to VCC(MAX), TA = -40°C to +85°C, unless otherwise noted. Typical values are at VCC = 3.3V, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 1 μA μA Input Leakage ILI (Note 3) I/O Leakage ILO (Note 4) VCC > 2V; VOL = 0.4V VCC < 2V; VOL = 0.2 x VCC 1 3.0 3.0 VCC > 2V; VOL = 0.4V 1.71V < VCC < 2V; VOL = 0.2 VCC 1.3V < VCC < 1.71V; VOL = 0.2 VCC DS1338-18 DS1338-3 VCC ≤ 3.63V DS1338-33 3.63V < VCC ≤ 5.5V DS1338-18 DS1338-3 VCC ≤ 3.63V DS1338-33 3.63V < VCC ≤ 5.5V 3.0 SDA Logic 0 Output SQW/OUT Logic 0 Output Active Supply Current (Note 5) Standby Current (Note 6) VBAT Leakage Current (VCC Active) IOLSDA IOLSQW ICCA ICCS IBATLKG 3.0 75 110 120 mA 250 μA 150 200 200 μA 325 60 80 85 100 125 125 μA 200 25 2 of 16 mA 100 nA DS1338 I2C RTC with 56-Byte NV RAM DC ELECTRICAL CHARACTERISTICS (VCC = 0V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at VBAT = 3.0V, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL VBAT Current (OSC ON); VBAT = 3.7V, SQW/OUT OFF (Note 7) MIN TYP MAX UNITS IBATOSC1 800 1200 nA VBAT Current (OSC ON); VBAT = 3.7V, SQW/OUT ON (32kHz) (Note 7) IBATOSC2 1025 1400 nA VBAT Data-Retention Current (Osc Off); VBAT = 3.7V (Note 7) IBATDAT 10 100 nA AC ELECTRICAL CHARACTERISTICS (VCC = VCC(MIN) to VCC(MAX), TA = -40°C to +85°C) (Note 1) PARAMETER SYMBOL SCL Clock Frequency fSCL Bus Free Time Between STOP and START Condition tBUF Hold Time (Repeated) START Condition (Note 8) tHD:STA LOW Period of SCL Clock tLOW HIGH Period of SCL Clock tHIGH Setup Time for Repeated START Condition tSU:STA Data Hold Time (Notes 9, 10) tHD:DAT Data Setup Time (Note 11) tSU:DAT Rise Time of Both SDA and SCL Signals (Note 12) tR Fall Time of Both SDA and SCL Signals (Note 12) tF Setup Time for STOP Condition tSU:STO CONDITION MIN Fast mode Standard mode 100 0 Fast mode 1.3 Standard mode 4.7 Fast mode 0.6 Standard mode 4.0 Fast mode 1.3 Standard mode 4.7 Fast mode 0.6 Standard mode 4.0 Fast mode 0.6 Standard mode 4.7 Fast mode 0 Standard mode 0 Fast mode 100 Standard mode 250 TYP MAX UNITS 400 100 kHz μs μs μs μs μs 0.9 ns Fast mode 20 + 0.1CB 300 Standard mode 20 + 0.1CB 1000 Fast mode 20 + 0.1CB 300 Standard mode 20 + 0.1CB 300 Fast mode 0.6 Standard mode 4.0 μs ns ns μs Capacitive Load for Each Bus Line CB (Note 12) 400 pF I/O Capacitance (SDA, SCL) CI/O (Note 13) 10 pF Oscillator Stop Flag (OSF) Delay tOSF (Note 14) 3 of 16 100 ms DS1338 I2C RTC with 56-Byte NV RAM POWER-UP/POWER-DOWN CHARACTERISTICS (TA = -40°C to +85°C) (Note 1, Figure 1) PARAMETER SYMBOL MIN TYP MAX UNITS 2 ms Recovery at Power-Up (Note 15) tREC VCC Fall Time; VPF(MAX) to VPF(MIN) tVCCF 300 μs VCC Rise Time; VPF(MIN) to VPF(MAX) tVCCR 0 μs Warning: Negative undershoots below -0.3V while the part is in battery-backed mode may cause loss of data. Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: Note 8: Note 9: Note 12: Limits at -40°C are guaranteed by design and not production tested. All voltages are referenced to ground. SCL only. SDA and SQW/OUT. ICCA—SCL clocking at max frequency = 400kHz. 2 Specified with the I C bus inactive. Measured with a 32.768kHz crystal attached to X1 and X2. After this period, the first clock pulse is generated. A device must internally provide a hold time of at least 300ns for the SDA signal (referred to the VIH(MIN) of the SCL signal) to bridge the undefined region of the falling edge of SCL. The maximum tHD:DAT need only be met if the device does not stretch the LOW period (tLOW ) of the SCL signal. A fast-mode device can be used in a standard-mode system, but the requirement tSU:DAT ≥ to 250ns must then be met. This is automatically the case if the device does not stretch the LOW period of the SCL signal. If such a device does stretch the LOW period of the SCL signal, it must output the next data bit to the SDA line tR(MAX) + tSU:DAT = 1000 + 250 = 1250ns before the SCL line is released. CB—total capacitance of one bus line in pF. Note 13: Guaranteed by design. Not production tested. Note 14: The parameter tOSF is the time period the oscillator must be stopped for the OSF flag to be set over the voltage range of 0.0V ≤ VCC ≤ VCC(MAX) and 1.3V ≤ VBAT ≤ 3.7V. This delay applies only if the oscillator is enabled and running. If the oscillator is disabled or stopped, no power-up delay occurs. Note 10: Note 11: Note 15: Figure 1. Power-Up/Power-Down Timing VCC VPF(MAX) VPF(MIN) t VCCR t VCCF tREC INPUTS RECOGNIZED DON'T CARE RECOGNIZED HIGH-Z OUTPUTS VALID VALID 4 of 16 DS1338 I2C RTC with 56-Byte NV RAM Figure 2. Timing Diagram Figure 3. Block Diagram X1 1Hz/4.096kHz/8.192kHz/32.768kHz CL MUX/ BUFFER 1Hz X2 CL OSCILLATOR AND DIVIDER "C" VERSION ONLY CONTROL LOGIC VCC GND POWER CONTROL VBAT Dallas Semiconductor DS1338 SCL SDA SERIAL BUS INTERFACE AND ADDRESS REGISTER RAM (56 X 8) CLOCK, CALENDAR, AND CONTROL REGISTERS USER BUFFER (7 BYTES) 5 of 16 SQW/OUT DS1338 I2C RTC with 56-Byte NV RAM TYPICAL OPERATING CHARACTERISTICS IBAT vs. VBAT ICC vs. VCC V CC=0V RS1=RS0=1 250 SCL=400kHz 225 1100 1050 1000 950 200 IBATOSC2 SQWE = 1) SUPPLY CURRENT (uA) SUPPLY CURRENT (nA) 1250 1200 1150 ( IBATOSC1 (SQWE = 0) 900 850 800 750 175 SCL=SDA=0Hz 150 125 100 700 650 600 550 75 50 1.3 1.8 2.3 2.8 3.3 3.8 VBAT (V) 4.3 4.8 IBAT vs. Temperature 5.3 1.8 2.3 2.8 3.3 3.8 VCC (V) 4.3 4.8 Oscillator Frequency vs. Supply Voltage V CC=0V VBAT = 3.0V 5.3 V CC=0V 32768.5 1000 32768.4 950 SUPPLY CURRENT (nA) 900 FREQUENCY (Hz) SQWE=1 850 SQWE=0 800 750 32768.3 32768.2 32768.1 700 32768.0 650 32767.9 600 -40 -20 0 20 40 TEMPERATURE (°C) 60 1.3 80 6 of 16 1.8 2.3 2.8 3.3 3.8 4.3 Oscillator Supply Voltage (V) 4.8 DS1338 I2C RTC with 56-Byte NV RAM PIN DESCRIPTION PIN NAME 8 16 1 — X1 2 — X2 FUNCTION 32.768kHz Crystal Connections. The internal oscillator circuitry is designed for operation with a crystal having a specified load capacitance (CL) of 12.5pF. An external 32.768kHz oscillator can also drive the DS1338. In this configuration, the X1 pin is connected to the external oscillator signal and the X2 pin is floated. Note: For more information about crystal selection and crystal layout considerations, refer to Application Note 58: Crystal Considerations with Dallas Real-Time Clocks. Backup Supply Input for Lithium Cell or Other Energy Source. Battery voltage must be held between the minimum and maximum limits for proper operation. Diodes placed in series between the backup source and the VBAT pin may prevent proper operation. If a backup supply is not required, VBAT must be grounded. UL recognized to ensure against reverse charging when used with a lithium cell. For more information, visit www.maxim-ic.com/qa/info/ul. Ground. DC power is provided to the device on these pins. VCC is the primary power input. When voltage is applied within normal limits, the device is fully accessible and data can be written and read. When a backup supply is connected to the device and VCC is below VPF, reads and writes are inhibited. However, the timekeeping function continues unaffected by the lower input voltage. 3 14 VBAT 4 15 GND 5 16 SDA Serial Data. Input/output pin for the I2C serial interface. It is open drain and requires an external pullup resistor. 6 1 SCL Serial Clock. Used to synchronize data movement on the serial interface 7 2 SQW/OUT Square-Wave/Output Driver. When enabled and the SQWE bit set to 1, the SQW/OUT pin outputs one of four square-wave frequencies (1Hz, 4kHz, 8kHz, 32kHz). It is open drain and requires an external pullup resistor. Operates with either VCC or VBAT applied. 8 3 VCC Primary Power Supply. When voltage is applied within normal limits, the device is fully accessible and data can be written and read. When a backup supply is connected to the device and VCC is below VPF, reads and writes are inhibited. The backup supply maintains the timekeeping function while VCC is absent. — 4–13 N.C. No Connection. These pins are not connected internally, but must be grounded for proper operation. DETAILED DESCRIPTION The DS1338 serial RTC is a low-power, full BCD clock/calendar plus 56 bytes of NV SRAM. Address and data are transferred serially through an I2C interface. The clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The end of the month date 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 AM/PM indicator. The DS1338 has a built-in power-sense circuit that detects power failures and automatically switches to the VBAT supply. 7 of 16 DS1338 I2C RTC with 56-Byte NV RAM OPERATION The DS1338 operates as a slave device on the serial bus. Access is obtained by implementing a START condition and providing a device identification code, followed by data. Subsequent registers can be accessed sequentially until a STOP condition is executed. The device is fully accessible and data can be written and read when VCC is greater than VPF. However, when VCC falls below VPF, the internal clock registers are blocked from any access. If VPF is less than VBAT, the device power is switched from VCC to VBAT when VCC drops below VPF. If VPF is greater than VBAT, the device power is switched from VCC to VBAT when VCC drops below VBAT. The oscillator and timekeeping functions are maintained from the VBAT source until VCC is returned to nominal levels. The block diagram (Figure 3) shows the main elements of the DS1338. An enable bit in the seconds register controls the oscillator. Oscillator startup times are highly dependent upon crystal characteristics, PC board leakage, and layout. High ESR and excessive capacitive loads are the major contributors to long start-up times. A circuit using a crystal with the recommended characteristics and proper layout usually starts within 1 second. POWER CONTROL The power-control function is provided by a precise, temperature-compensated voltage reference and a comparator circuit that monitors the VCC level. The device is fully accessible and data can be written and read when VCC is greater than VPF. However, when VCC falls below VPF, the internal clock registers are blocked from any access. If VPF is less than VBAT, the device power is switched from VCC to VBAT when VCC drops below VPF. If VPF is greater than VBAT, the device power is switched from VCC to VBAT when VCC drops below VBAT. The registers are maintained from the VBAT source until VCC is returned to nominal levels (Table 1). After VCC returns above VPF, read and write access is allowed after tREC (Figure 1). Table 1. Power Control SUPPLY CONDITION READ/WRITE ACCESS POWERED BY VCC < VPF, VCC < VBAT VCC < VPF, VCC > VBAT VCC > VPF, VCC < VBAT VCC > VPF, VCC > VBAT No No Yes Yes VBAT VCC VCC VCC OSCILLATOR CIRCUIT The DS1338 uses an external 32.768kHz crystal. The oscillator circuit does not require any external resistors or capacitors to operate. Table 2 specifies several crystal parameters for the external crystal. Figure 3 shows a functional schematic of the oscillator circuit. The startup time is usually less than 1 second when using a crystal with the specified characteristics. Table 2. Crystal Specifications* PARAMETER Nominal Frequency SYMBOL fO Series Resistance ESR Load Capacitance CL MIN TYP MAX 32.768 kHz 50 12.5 UNITS kΩ pF *The crystal, traces, and crystal input pins should be isolated from RF generating signals. Refer to Application Note 58: Crystal Considerations for Dallas Real-Time Clocks for additional specifications. 8 of 16 DS1338 I2C RTC with 56-Byte NV RAM CLOCK ACCURACY The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match between the capacitive load of the oscillator circuit and the capacitive load for which the crystal was trimmed. Crystal frequency drift caused by temperature shifts creates additional error. External circuit noise coupled into the oscillator circuit can result in the clock running fast. Figure 4 shows a typical PC board layout for isolating the crystal and oscillator from noise. Refer to Application Note 58: Crystal Considerations with Dallas Real-Time Clocks for detailed information. DS1338C ONLY The DS1338C integrates a standard 32,768Hz crystal in the package. Typical accuracy at nominal VCC and +25°C is approximately 10ppm. Refer to Application Note 58 for information about crystal accuracy vs. temperature. Figure 4. Typical PC Board Layout for Crystal LOCAL GROUND PLANE (LAYER 2) X1 CRYSTAL X2 GND NOTE: AVOID ROUTING SIGNALS IN THE CROSSHATCHED AREA (UPPER LEFT-HAND QUADRANT) OF THE PACKAGE UNLESS THERE IS A GROUND PLANE BETWEEN THE SIGNAL LINE AND THE PACKAGE. RTC AND RAM ADDRESS MAP Table 3 shows the address map for the RTC and RAM registers. The RTC registers and control register are located in address locations 00h to 07h. The RAM registers are located in address locations 08h to 3Fh. During a multibyte access, when the register pointer reaches 3Fh (the end of RAM space) it wraps around to location 00h (the beginning of the clock space). On an I2C START, STOP, or register pointer incrementing to location 00h, the current time and date is transferred to a second set of registers. The time and date in the secondary registers are read in a multibyte data transfer, while the clock continues to run. This eliminates the need to re-read the registers in case of an update of the main registers during a read. CLOCK AND CALENDAR The time and calendar information is obtained by reading the appropriate register bytes. See Figure 6 for the RTC registers. The time and calendar are set or initialized by writing the appropriate register bytes. The contents of the time and calendar registers are in the BCD format. Bit 7 of Register 0 is the clock halt (CH) bit. When this bit is set to 1, the oscillator is disabled. When cleared to 0, the oscillator is enabled. The clock can be halted whenever the timekeeping functions are not required, which decreases VBAT current. The day-of-week register increments at midnight. Values that correspond to the day of week are user-defined 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 (user) buffers are used to prevent errors when the internal registers update. When reading the time and date registers, the user buffers are synchronized to the internal registers on any start or stop and when the register pointer rolls over to zero. The countdown chain is reset 9 of 16 DS1338 I2C RTC with 56-Byte NV RAM whenever the seconds register is written. Write transfers occur on the acknowledge from the DS1338. Once the countdown chain is reset, to avoid rollover issues the remaining time and date registers must be written within 1 second. The 1Hz square-wave output, if enabled, transitions high 500ms after the seconds data transfer, provided the oscillator is already running. Note that the initial power-on state of all registers, unless otherwise specified, is not defined. Therefore, it is important to enable the oscillator (CH = 0) during initial configuration. The DS1338 runs 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 second 10-hour bit (20–23 hours). If the 12/24-hour mode select is changed, the hours register must be re-initialized to the new format. On an I2C START, the current time is transferred to a second set of registers. The time information is read from these secondary registers, while the clock continues to run. This eliminates the need to re-read the registers in case of an update of the main registers during a read. Table 3. RTC and RAM Address Map ADDRESS BIT 7 00H 01H CH 0 02H 0 12/24 03H 04H 0 0 05H 0 06H 07H OUT BIT 6 BIT 5 10 Seconds 10 Minutes AM/PM BIT 4 10 Hour 10 Hour 0 0 0 0 0 0 BIT 3 BIT 2 FUNCTION RANGE Seconds Minutes Seconds Minutes Hour Hours SQWE Date Day Date Month Month 01–12 Year Year Control 00–99 RAM 56 x 8 00H–FFH Day 10 Month 0 08H–3FH Note: Bits listed as “0” always read as a 0. 10 of 16 BIT 0 00–59 00–59 1–12 +AM/PM 00–23 1–7 01–31 0 10 Date 10 Year 0 OSF BIT 1 0 RS1 RS0 DS1338 I2C RTC with 56-Byte NV RAM CONTROL REGISTER (07H) The control register controls the operation of the SQW/OUT pin and provides oscillator status. Bit # Name POR BIT 7 OUT 1 BIT 6 0 0 BIT 5 OSF 1 BIT 4 SQWE 1 BIT 3 0 0 BIT 2 0 0 BIT 1 RS1 1 BIT 0 RS0 1 Bit 7: Output Control (OUT). Controls the output level of the SQW/OUT pin when the square-wave output is disabled. If SQWE = 0, the logic level on the SQW/OUT pin is 1 if OUT = 1; it is 0 if OUT = 0. Bit 5: Oscillator Stop Flag (OSF). A logic 1 in this bit indicates that the oscillator has stopped or was stopped for some time period and can be used to judge the validity of the clock and calendar data. This bit is edge triggered, and is set to logic 1 when the internal circuitry senses the oscillator has transitioned from a normal run state to a STOP condition. The following are examples of conditions that may cause the OSF bit to be set: 1) The first time power is applied. 2) The voltage present on VCC and VBAT are insufficient to support oscillation. 3) The CH bit is set to 1, disabling the oscillator. 4) External influences on the crystal (i.e., noise, leakage, etc.). This bit remains at logic 1 until written to logic 0. This bit can only be written to logic 0. Attempting to write OSF to logic 1 leaves the value unchanged. Bit 4: Square-Wave Enable (SQWE). When set to logic 1, this bit enables the oscillator output to operate with either VCC or VBAT applied. The frequency of the square-wave output depends upon the value of the RS0 and RS1 bits. Bits 1 and 0: Rate Select (RS1 and RS0). These bits control the frequency of the square-wave output when the square-wave output has been enabled. The table below lists the square-wave frequencies that can be selected with the RS bits. Square-Wave Output OUT X X X X 0 1 RS1 0 0 1 1 X X RS0 0 1 0 1 X X SQW OUTPUT 1Hz 4.096kHz 8.192kHz 32.768kHz 0 1 SQWE 1 1 1 1 0 0 11 of 16 DS1338 I2C RTC with 56-Byte NV RAM I2C SERIAL DATA BUS The DS1338 supports the I2C protocol. A device that sends data onto the bus is defined as a transmitter and a device receiving data is a receiver. The device that controls the message is called a master. The devices that are controlled by the master are referred to as slaves. The bus must be controlled by a master device, which generates the serial clock (SCL), controls the bus access, and generates the START and STOP conditions. The DS1338 operates as a slave on the I2C bus. Within the bus specifications, a standard mode (100kHz maximum clock rate) and a fast mode (400kHz maximum clock rate) are defined. The DS1338 works in both modes. Connections to the bus are made through the open-drain I/O lines SDA and SCL. The following bus protocol has been defined (Figure 5). Data transfer can be initiated only when the bus is not busy. During data transfer, the data line must remain stable whenever the clock line is HIGH. Changes in the data line while the clock line is HIGH are interpreted as control signals. Accordingly, the following bus conditions have been defined: Bus not busy: Both data and clock lines remain HIGH. Start data transfer: A change in the state of the data line, from HIGH to LOW, while the clock is HIGH, defines a START condition. Stop data transfer: A change in the state of the data line, from LOW to HIGH, while the clock line is HIGH, defines the STOP condition. Data valid: The state of the data line represents valid data when, after a START condition, the data line is stable for the duration of the HIGH period of the clock signal. The data on the line must be changed during the LOW period of the clock signal. There is one clock pulse per bit of data. Each data transfer is initiated with a START condition and terminated with a STOP condition. The number of data bytes transferred between START and STOP conditions is not limited and is determined by the master device. The information is transferred byte-wise and each receiver acknowledges with a ninth bit. Acknowledge: Each receiving device, when addressed, is obliged to generate an acknowledge after the reception of each byte. The master device must generate an extra clock pulse that is associated with this acknowledge bit. A device that acknowledges must pull down the SDA line during the acknowledge clock pulse in such a way that the SDA line is stable LOW during the HIGH period of the acknowledge-related clock pulse. Of course, setup and hold times must be taken into account. A master must signal an end of data to the slave by not generating an acknowledge bit on the last byte that has been clocked out of the slave. In this case, the slave must leave the data line HIGH to enable the master to generate the STOP condition. Figure 5. Data Transfer on I2C Serial Bus 12 of 16 DS1338 I2C RTC with 56-Byte NV RAM Depending upon the state of the R/W bit, two types of data transfer are possible: 1) Data transfer from a master transmitter to a slave receiver. The master transmits the first byte (the slave address). Next follows a number of data bytes. The slave returns an acknowledge bit after each received byte. Data is transferred with the most significant bit (MSB) first. 2) Data transfer from a slave transmitter to a master receiver. The master transmits the first byte (the slave address). The slave then returns an acknowledge bit, which is followed by the slave transmitting a number of data bytes. The master returns an acknowledge bit after all received bytes other than the last byte. At the end of the last received byte, a “not acknowledge” is returned. The master device generates all of the serial clock pulses and the START and STOP conditions. A transfer is ended with a STOP condition or with a repeated START condition. Since a repeated START condition is also the beginning of the next serial transfer, the bus is not released. Data is transferred with the most significant bit (MSB) first. The DS1338 can operate in the following two modes: 1) Slave receiver mode (write mode): Serial data and clock are received through SDA and SCL. An acknowledge bit is transmitted after each byte is received. START and STOP conditions are recognized as the beginning and end of a serial transfer. Hardware performs address recognition after reception of the slave address and direction bit (Figure 6). The slave address byte is the first byte received after the master generates the START condition. The slave address byte contains the 7-bit DS1338 address—1101000— followed by the direction bit (R/W), which, for a write, is 0. After receiving and decoding the slave address byte, the slave outputs an acknowledge on the SDA line. After the DS1338 acknowledges the slave address and write bit, the master transmits a register address to the DS1338. This sets the register pointer on the DS1338, with DS1338 acknowledging the transfer. The master may then transmit zero or more bytes of data, with the DS1338 acknowledging each byte received. The register pointer increments after each data byte is transferred. The master generates a STOP condition to terminate the data write. 2) Slave transmitter mode (read mode): The first byte is received and handled as in the slave receiver mode. However, in this mode, the direction bit indicates that the transfer direction is reversed. The DS1338 transmits serial data on SDA while the serial clock is input on SCL. START and STOP conditions are recognized as the beginning and end of a serial transfer (Figure 7). The slave address byte is the first byte received after the master generates the START condition. The slave address byte contains the 7-bit DS1338 address— 1101000—followed by the direction bit (R/W), which, for a read, is 1. After receiving and decoding the slave address byte, the slave outputs an acknowledge on the SDA line. The DS1338 then starts transmitting data using the register address pointed to by the register pointer. If the register pointer is not set before the initiation of a read mode, the first address that is read is the last one stored in the register pointer. The register pointer is incremented after each byte is transferred. The DS1338 must receive a “not acknowledge” to end a read. 13 of 16 DS1338 I2C RTC with 56-Byte NV RAM <Slave Address> S <R/W> Figure 6. Data Write—Slave Receiver Mode <Word Address (n)> 1101000 0 A S - START A - ACKNOWLEDGE (ACK) P - STOP <Data (n)> XXXXXXXX A <Data (n+X)> <Data (n+1)> XXXXXXXX A XXXXXXXX A ... XXXXXXXX A P MASTER TO SLAVE DATA TRANSFERRED (X+1 BYTES + ACKNOWLEDGE) SLAVE TO MASTER <R/W> Figure 7. Data Read (From Current Pointer Location)—Slave Transmitter Mode <Slave Address> S <Data (n)> <Data (n+2)> <Data (n+1)> <Data (n+X)> 1 A XXXXXXXX A XXXXXXXX A XXXXXXXX A ... XXXXXXXX A P 1101000 S - START A - ACKNOWLEDGE (ACK) P - STOP MASTER TO SLAVE DATA TRANSFERRED (X+1 BYTES + ACKNOWLEDGE) NOTE: LAST DATA BYTE IS FOLLOWED BY A NACK SLAVE TO MASTER A - NOT ACKNOWLEDGE (NACK) S 1101000 0 A <Data (n)> XXXXXXXX A <Word Address (n)> <Data (n+1)> XXXXXXXX A S - START SR - REPEATED START A - ACKNOWLEDGE (ACK) P - STOP A - NOT ACKNOWLEDGE (NACK) <Slave Address> XXXXXXXX A Sr 1101000 1 A <Data (n+2)> <Data (n+X)> XXXXXXXX A ... MASTER TO SLAVE SLAVE TO MASTER 14 of 16 <R/W> <R/W> Figure 8. Data Read (Write Pointer, Then Read—Slave Receive and Transmit XXXXXXXX A P DATA TRANSFERRED (X+1 BYTES + ACKNOWLEDGE) NOTE: LAST DATA BYTE IS FOLLOWED BY A NACK DS1338 I2C RTC with 56-Byte NV RAM HANDLING, PC BOARD LAYOUT, AND ASSEMBLY The DS1338C package contains a quartz tuning-fork crystal. Pick-and-place equipment may be used, but precautions should be taken to ensure that excessive shocks are avoided. Ultrasonic cleaning should be avoided to prevent damage to the crystal. Exposure to reflow is limited to 2 times maximum. Avoid running signal traces under the package, unless a ground plane is placed between the package and the signal line. All N.C. (no connect) pins must be connected to ground. The leaded 16-SO package may be reflowed as long as the peak temperature does not exceed 240°C. Peak reflow temperature (≥ 230°C) duration should not exceed 10 seconds, and the total time above 200°C should not exceed 40 seconds (30 seconds nominal). The RoHS and lead-free/RoHS packages may be reflowed using a reflow profile that complies with JEDEC J-STD020. Moisture-sensitive packages are shipped from the factory dry-packed. Handling instructions listed on the package label must be followed to prevent damage during reflow. Refer to the IPC/JEDEC J-STD-020 standard for moisturesensitive device (MSD) classifications. 15 of 16 DS1338 I2C RTC with 56-Byte NV RAM PIN CONFIGURATIONS TOP VIEW TOP VIEW X2 VBAT GND 1 8 2 7 3 4 DS1338 X1 VCC SCL SQW/OUT SQW/OUT SDA DS1338C Vcc GND VBAT N.C. N.C. 6 SCL N.C. N.C. 5 SDA N.C. N.C. N.C. N.C. N.C. N.C. SO, µSOP SO (300 mils) CHIP INFORMATION TRANSISTOR COUNT: 12,231 PROCESS: CMOS THERMAL INFORMATION PART 8 SO 8 µSOP 16 SO THETA-JA (°C/W) 170 229 73 THETA-JC (°C/W) 40 39 23 PACKAGE INFORMATION For the latest package outline information, go to www.maxim-ic.com/DallasPackInfo. PACKAGE TYPE 8-pin SO 8-pin µSOP 16-pin SO DOCUMENT NUMBER 56-G2008-001 21-0036 56-G4009-001 16 of 16 Maxim/Dallas Semiconductor cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim/Dallas Semiconductor product. No circuit patent licenses are implied. Maxim/Dallas Semiconductor reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2007 Maxim Integrated Products The Maxim logo is a registered trademark of Maxim Integrated Products, Inc. The Dallas logo is a registered trademark of Dallas Semiconductor Corporation.