DS1306 Serial Alarm Real-Time Clock www.maxim-ic.com FEATURES § § § § § § § § § § § § Real-Time Clock (RTC) Counts Seconds, Minutes, Hours, Date of the Month, Month, Day of the Week, and Year with Leap-Year Compensation Valid Up to 2100 96-Byte, Battery-Backed NV RAM for Data Storage Two Time-of-Day Alarms, Programmable on Combination of Seconds, Minutes, Hours, and Day of the Week 1Hz and 32.768kHz Clock Outputs Supports Motorola SPI™ (Serial Peripheral Interface) Modes 1 and 3 or Standard 3-Wire Interface Burst Mode for Reading/Writing Successive Addresses in Clock/RAM Dual-Power Supply Pins for Primary and Backup Power Supplies Optional Trickle Charge Output to Backup Supply 2.0V to 5.5V Operation Optional Industrial Temperature Range: -40°C to +85°C Available in Space-Efficient, 20-Pin TSSOP Package Underwriters Laboratory (UL) Recognized PIN CONFIGURATIONS 1 2 3 4 5 6 7 8 9 10 VCC2 VBAT X1 N.C. X2 N.C. INT0 INT1 1Hz GND VCC1 N.C. 32kHz VCCIF SDO SDI SCLK N.C. CE SERMODE 20 19 18 17 16 15 14 13 12 11 TSSOP (4.4mm) 1 16 VCC1 VBAT 2 15 32kHz X1 3 14 VCCIF X2 4 13 SDO 5 12 SDI INT1 6 11 SCLK 1Hz 7 10 CE GND 8 9 VCC2 INT0 SERMODE DIP (300 mils) Package Dimension Information can be found at: www.maxim-ic.com/DallasPackInfo TYPICAL OPERATING CIRCUIT SPI is a trademark of Motorola, Inc. 1 of 21 REV: 071105 DS1306 ORDERING INFORMATION PART DS1306 DS1306+ DS1306N DS1306N+ DS1306E+ DS1306EN+ DS1306EN+T&R DS1306E+T&R DS1306E DS1306EN DS1306EN/T&R DS1306E/T&R TEMP RANGE PIN-PACKAGE TOP MARK* 0°C to +70°C 0°C to +70°C -40°C to +85°C 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C 0°C to +70°C DS1306 DS1306 + DS1306N DS1306N + DS1306 + DS1306N + DS1306N + DS1306 + DS1306 DS1306N DS1306N DS1306 16 DIP (300 mils) 16 DIP (300 mils) 16 DIP (300 mils) 16 DIP (300 mils) 20 TSSOP (173 mils) 20 TSSOP (173 mils) 20 TSSOP (173 mils) 20 TSSOP (173 mils) 20 TSSOP (173 mils) 20 TSSOP (173 mils) 20 TSSOP (173 mils) 20 TSSOP (173 mils) + Denotes a lead-free/RoHS-compliant device. * An “N” on the top mark indicates an industrial device. PIN DESCRIPTION PIN TSSOP DIP NAME 1 1 VCC2 2 2 VBAT 3 3 X1 5 4 X2 7 5 INT0 8 6 INT1 FUNCTION Backup Power Supply. This is the secondary power supply pin. In systems using the trickle charger, the rechargeable energy source is connected to this pin. Battery Input for Any Standard +3V Lithium Cell or Other Energy Source. If not used, VBAT must be connected to ground. Diodes must not be placed in series between VBAT and the battery, or improper operation will result. UL recognized to ensure against reverse charging current when used in conjunction with a lithium battery. See “Conditions of Acceptability” at www.maxim-ic.com/TechSupport/QA/ntrl.htm. Connections for Standard 32.768kHz Quartz Crystal. The internal oscillator is designed for operation with a crystal having a specified load capacitance of 6pF. For more information on crystal selection and crystal layout considerations, refer to Application Note 58, “Crystal Considerations with Dallas Real-Time Clocks.” The DS1306 can also be driven by an external 32.768kHz oscillator. In this configuration, the X1 pin is connected to the external oscillator signal and the X2 pin is floated. Active-Low Interrupt 0 Output. The INT0 pin is an active-low output of the DS1306 that can be used as an interrupt input to a processor. The INT0 pin can be programmed to be asserted by Alarm 0. The INT0 pin remains low as long as the status bit causing the interrupt is present and the corresponding interrupt enable bit is set. The INT0 pin operates when the DS1306 is powered by VCC1, VCC2, or VBAT. The INT0 pin is an open-drain output and requires an external pullup resistor. Interrupt 1 Output. The INT1 pin is an active high output of the DS1306 that can be used as an interrupt input to a processor. The INT1 pin can be programmed to be asserted by Alarm 1. When an alarm condition is present, the INT1 pin generates a 62.5ms active-high pulse. The INT1 pin operates only when the DS1306 is powered by VCC2 or VBAT. When active, the INT1 pin is internally pulled up to VCC2 or VBAT. When inactive, the INT1 pin is internally pulled low. 2 of 21 DS1306 PIN DESCRIPTION (continued) PIN TSSOP DIP 9 7 10 8 11 9 12 10 14 11 15 12 16 13 17 14 18 15 20 16 4, 6, 13, 19 — NAME FUNCTION 1Hz Output. The 1Hz pin provides a 1Hz square wave output. This output is active when the 1 Hz bit in the control register is a logic 1. Both INT0 and 1Hz 1Hz pins are open-drain outputs. The interrupt, 1Hz signal, and the internal clock continue to run regardless of the level of VCC (as long as a power source is present). GND Ground Serial Interface Mode. The SERMODE pin offers the flexibility to choose between two serial interface modes. When connected to GND, standard SERMODE 3-wire communication is selected. When connected to VCC, SPI communication is selected. Chip Enable. The chip enable signal must be asserted high during a read or CE a write for both 3-wire and SPI communication. This pin has an internal 55k pulldown resistor (typical). Serial Clock. SCLK is used to synchronize data movement on the serial SCLK interface for either the SPI or 3-wire interface. Serial Data In. When SPI communication is selected, the SDI pin is the serial data input for the SPI bus. When 3-wire communication is selected, SDI this pin must be tied to the SDO pin (the SDI and SDO pins function as a single I/O pin when tied together). Serial Data Out. When SPI communication is selected, the SDO pin is the serial data output for the SPI bus. When 3-wire communication is selected, SDO this pin must be tied to the SDI pin (the SDI and SDO pins function as a single I/O pin when tied together). VCCIF provides the logic high level. Interface Logic Power-Supply Input. The VCCIF pin allows the DS1306 to drive SDO and 32kHz output pins to a level that is compatible with the VCCIF interface logic, thus allowing an easy interface to 3V logic in mixed supply systems. This pin is physically connected to the source connection of the pchannel transistors in the output buffers of the SDO and 32kHz pins. 32.768kHz Output. The 32kHz pin provides a 32.768kHz output. This 32kHz signal is always present. VCCIF provides the logic high level. Primary Power Supply. DC power is provided to the device on this pin. VCC1 VCC1 is the primary power supply. N.C. No Connection 3 of 21 DS1306 DESCRIPTION The DS1306 serial alarm real-time clock (RTC) provides a full binary coded decimal (BCD) clock calendar that is accessed by a simple serial 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 24hour or 12-hour format with AM/PM indicator. In addition, 96 bytes of NV RAM are provided for data storage. An interface logic-power supply input pin (VCCIF) allows the DS1306 to drive SDO and 32kHz pins to a level that is compatible with the interface logic. This allows an easy interface to 3V logic in mixed supply systems. The DS1306 offers dual-power supplies as well as a battery-input pin. The dual-power supplies support a programmable trickle charge circuit that allows a rechargeable energy source (such as a super cap or rechargeable battery) to be used for a backup supply. The VBAT pin allows the device to be backed up by a non-rechargeable battery. The DS1306 is fully operational from 2.0V to 5.5V. Two programmable time-of-day alarms are provided by the DS1306. Each alarm can generate an interrupt on a programmable combination of seconds, minutes, hours, and day. “Don’t care” states can be inserted into one or more fields if it is desired for them to be ignored for the alarm condition. A 1Hz and a 32kHz clock output are also available. The DS1306 supports a direct interface to SPI serial data ports or standard 3-wire interface. An easy-touse address and data format is implemented in which data transfers can occur 1 byte at a time or in multiple-byte burst mode. OPERATION The block diagram in Figure 1 shows the main elements of the serial alarm RTC. The following paragraphs describe the function of each pin. Figure 1. BLOCK DIAGRAM 1Hz 4 of 21 DS1306 RECOMMENDED LAYOUT FOR CRYSTAL Local ground plane (Layer 2) X1 crystal X2 GND 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. Additional error is added by crystal frequency drift caused by temperature shifts. External circuit noise coupled into the oscillator circuit can result in the clock running fast. Refer to Application Note 58: Crystal Considerations with Dallas Real-Time Clocks for detailed information. CLOCK, CALENDAR, AND ALARM The time and calendar information is obtained by reading the appropriate register bytes. The RTC registers are illustrated in Figure 2. The time, calendar, and alarm are set or initialized by writing the appropriate register bytes. Note that some bits are set to 0. These bits always read 0 regardless of how they are written. Also note that registers 12h to 1Fh (read) and registers 92h to 9Fh are reserved. These registers always read 0 regardless of how they are written. The contents of the time, calendar, and alarm registers are in the BCD format.. Values in the day register that correspond to the day of the week are user-defined, but must be sequential (e.g. if 1 equals Sunday, 2 equals Monday and so on). The day register increments at midnight. Illogical time and date entries result in undefined operation. WRITING TO THE CLOCK REGISTERS The internal time and date registers continue to increment during write operations. However, the countdown chain is reset when the seconds register is written. Writing the time and date registers within one second after writing the seconds register ensures consistent data. Terminating a write before the last bit is sent aborts the write for that byte. READING FROM THE CLOCK REGISTERS Buffers are used to copy the time and date register at the beginning of a read. When reading in burst mode, the user copy is static while the internal registers continue to increment. 5 of 21 DS1306 Figure 2. RTC REGISTERS AND ADDRESS MAP HEX ADDRESS READ 00H 01H WRITE 80H 81H 02H 82H Bit 7 0 0 0 03H 04H 05H 06H 07H 08H 83H 84H 85H 86H 87H 88H 0 0 0 M M 09H 89H M Bit6 Bit5 Bit4 10 SEC 10 MIN P 12 10-HR A 24 10 0 0 0 0 10-DATE 0 10-MONTH 10-YEAR 10-SEC ALARM 0 10-MIN ALARM 0 P 12 10-HR A 24 10 0AH 8AH M 0 0BH 0CH 8BH 8CH M M 0DH 8DH M 10 SEC ALARM 1 10 MIN ALARM 1 P 12 10-HR A 24 10 0 0 0 0EH 8EH 0FH 10H 11H 12–1FH 8FH 90H 91H 92–9FH A0– FFH 20–7FH M Bit3 0 0 Bit2 Bit1 Bit0 SEC MIN HOURS 0 DAY DATE MONTH YEAR SEC ALARM 0 MIN ALARM 0 HOUR ALARM 0 RANGE 00–59 00–59 01–12 + P/A 00–23 01–07 1–31 01–12 00–99 00–59 00–59 01–12 + P/A 00–23 0 DAY ALARM 0 SEC ALARM 1 MIN ALARM 1 HOUR ALARM 1 0 DAY ALARM 1 — CONTROL REGISTER STATUS REGISTER TRICKLE CHARGER REGISTER RESERVED 96-BYTES USER RAM 01–07 00–59 00–59 01–12 + P/A 00–23 01–07 — — — — — Note: Range for alarm registers does not include mask’m’ bits. The DS1306 can be run in either 12-hour or 24-hour mode. Bit 6 of the hours register is defined as the 12- 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 to 23 hours). The DS1306 contains two time-of-day alarms. Time-of-day alarm 0 can be set by writing to registers 87h to 8Ah. Time-of-day Alarm 1 can be set by writing to registers 8 Bh to 8 Eh. Bit 7 of each of the time-ofday alarm registers are mask bits (Table 1). When all of the mask bits are logic 0, a time-of-day alarm only occurs once per week when the values stored in timekeeping registers 00h to 03h match the values stored in the time-of-day alarm registers. An alarm is generated every day when bit 7 of the day alarm register is set to a logic 1. An alarm is generated every hour when bit 7 of the day and hour alarm registers is set to a logic 1. Similarly, an alarm is generated every minute when bit 7 of the day, hour, and 6 of 21 DS1306 minute alarm registers is set to a logic 1. When bit 7 of the day, hour, minute, and seconds alarm registers is set to a logic 1, an alarm occurs every second. During each clock update, the RTC compares the Alarm 0 and Alarm 1 registers with the corresponding clock registers. When a match occurs, the corresponding alarm flag bit in the status register is set to a 1. If the corresponding alarm interrupt enable bit is enabled, an interrupt output is activated. Table 1. TIME-OF-DAY ALARM MASK BITS ALARM REGISTER MASK BITS (BIT 7) SECONDS MINUTES HOURS DAYS 1 1 1 1 0 1 1 1 0 0 1 1 0 0 0 1 0 0 0 0 FUNCTION Alarm once per second Alarm when seconds match Alarm when minutes and seconds match Alarm hours, minutes, and seconds match Alarm day, hours, minutes and seconds match SPECIAL PURPOSE REGISTERS The DS1306 has three additional registers (control register, status register, and trickle charger register) that control the real-time clock, interrupts, and trickle charger. CONTROL REGISTER (READ 0FH, WRITE 8FH) BIT7 0 BIT6 WP BIT5 0 BIT4 0 BIT3 0 BIT2 1Hz BIT1 AIE1 BIT0 AIE0 WP (Write Protect) – Before any write operation to the clock or RAM, this bit must be logic 0. When high, the write protect bit prevents a write operation to any register, including bits 0, 1, and 2 of the control register. Upon initial power-up, the state of the WP bit is undefined. Therefore, the WP bit should be cleared before attempting to write to the device. When WP is set, it must be cleared before any other control register bit can be written. 1Hz (1Hz Output Enable) – This bit controls the 1Hz output. When this bit is a logic 1, the 1Hz output is enabled. When this bit is a logic 0, the 1Hz output is high-Z. AIE0 (Alarm Interrupt Enable 0) – When set to a logic 1, this bit permits the interrupt 0 request flag (IRQF0) bit in the status register to assert INT0 . When the AIE0 bit is set to logic 0, the IRQF0 bit does not initiate the INT0 signal. AIE1 (Alarm Interrupt Enable 1) – When set to a logic 1, this bit permits the interrupt 1 request flag (IRQF1) bit in the status register to assert INT1. When the AIE1 bit is set to logic 0, the IRQF1 bit does not initiate an interrupt signal, and the INT1 pin is set to a logic 0 state. 7 of 21 DS1306 STATUS REGISTER (READ 10H) BIT7 0 BIT6 0 BIT5 0 BIT4 0 BIT3 0 BIT2 0 BIT1 IRQF1 BIT0 IRQF0 IRQF0 (Interrupt 0 Request Flag) – A logic 1 in the interrupt request flag bit indicates that the current time has matched the Alarm 0 registers. If the AIE0 bit is also a logic 1, the INT0 pin goes low. IRQF0 is cleared when the address pointer goes to any of the Alarm 0 registers during a read or write. IRQF0 is activated when the device is powered by VCC1, VCC2, or VBAT. IRQF1 (Interrupt 1 Request Flag) – A logic 1 in the interrupt request flag bit indicates that the current time has matched the Alarm 1 registers. If the AIE1 bit is also a logic 1, the INT1 pin generates a 62.5ms active-high pulse. IRQF1 is cleared when the address pointer goes to any of the alarm 1 registers during a read or write. IRQF1 is activated only when the device is powered by VCC2 or VBAT. TRICKLE CHARGE REGISTER (READ 11H, WRITE 91H) This register controls the trickle charge characteristics of the DS1306. The simplified schematic of Figure 3 shows the basic components of the trickle charger. The trickle charge select (TCS) bits (bits 4–7) control the selection of the trickle charger. In order to prevent accidental enabling, only a pattern of 1010 enables the trickle charger. All other patterns disable the trickle charger. The DS1306 powers up with the trickle charger disabled. The diode select (DS) bits (bits 2–3) select whether one diode or two diodes are connected between VCC1 and VCC2. The diode select (DS) bits (bits 2–3) select whether one diode or two diodes are connected between VCC1 and VCC2. The resistor select (RS) bits select the resistor that is connected between VCC1 and VCC2. The resistor and diodes are selected by the RS and DS bits as shown in Table 2. Figure 3. PROGRAMMABLE TRICKLE CHARGER 8 of 21 DS1306 Table 2. TRICKLE CHARGER RESISTOR AND DIODE SELECT TCS Bit 7 TCS Bit 6 TCS Bit 5 TCS Bit 4 DS Bit 3 DS Bit 2 RS Bit 1 RS Bit 0 FUNCTION X X X X X X 0 0 Disabled X X X X 0 0 X X Disabled X X X X 1 1 X X Disabled 1 0 1 0 0 1 0 1 1 Diode, 2kΩ 1 0 1 0 0 1 1 0 1 Diode, 4kΩ 1 0 1 0 0 1 1 1 1 Diode, 8kΩ 1 0 1 0 1 0 0 1 2 Diodes, 2kΩ 1 0 1 0 1 0 1 0 2 Diodes, 4kΩ 1 0 1 0 1 0 1 1 2 Diodes, 8kΩ 0 1 0 1 1 1 0 0 Initial power-on state If RS is 00, the trickle charger is disabled independently of TCS. Diode and resistor selection is determined by the user according to the maximum current desired for battery or super cap charging. The maximum charging current can be calculated as illustrated in the following example. Assume that a system power supply of 5V is applied to VCC1 and a super cap is connected to VCC2. Also assume that the trickle charger has been enabled with one diode and resister R1 between VCC1 and VCC2. The maximum current IMAX would, therefore, be calculated as follows: IMAX = (5.0V - diode drop) / R1 » (5.0V - 0.7V) / 2kΩ » 2.2mA As the super cap charges, the voltage drop between VCC1 and VCC2 decreases and, therefore, the charge current decreases. POWER CONTROL Power is provided through the VCC1, VCC2, and VBAT pins. Three different power supply configurations are illustrated in Figure 4. Configuration 1 shows the DS1306 being backed up by a non-rechargeable energy source such as a lithium battery. In this configuration, the system power supply is connected to VCC1 and VCC2 is grounded. When VCC falls below VBAT the device switches into a low-current battery backup mode. Upon power-up, the device switches from VBAT to VCC when VCC is greater than VBAT + 0.2V. The device is write-protected whenever it is switched to VBAT. Configuration 2 illustrates the DS1306 being backed up by a rechargeable energy source. In this case, the VBAT pin is grounded, VCC1 is connected to the primary power supply, and VCC2 is connected to the secondary supply (the rechargeable energy source). The DS1306 operates from the larger of VCC1 or VCC2. When VCC1 is greater than VCC2 + 0.2V (typical), VCC1 powers the DS1306. When VCC1 is less than VCC2, VCC2 powers the DS1306. The DS1306 does not write-protect itself in this configuration. Configuration 3 shows the DS1306 in battery-operate mode, where the device is powered only by a single battery. In this case, the VCC1 and VBAT pins are grounded and the battery is connected to the VCC2 pin. Only these three configurations are allowed. Unused supply pins must be grounded. 9 of 21 DS1306 Figure 4. POWER SUPPLY CONFIGURATIONS CONFIGURATION 1: BACKUP SUPPLY IS NONRECHARGEABLE LITHIUM BATTERY NOTE: DEVICE IS WRITE-PROTECTED IF VCC < VCCTP. CONFIGURATION 2: BACKUP SUPPLY IS A RECHARGEABLE BATTERY OR SUPER CAPACITOR NOTE: DEVICE DOES NOT PROVIDE AUTOMATIC WRITE PROTECTION. CONFIGURATION 3: BATTERY OPERATE MODE 10 of 21 DS1306 SERIAL INTERFACE The DS1306 offers the flexibility to choose between two serial interface modes. The DS1306 can communicate with the SPI interface or with a standard 3-wire interface. The interface method used is determined by the SERMODE pin. When this pin is connected to VCC, SPI communication is selected. When this pin is connected to ground, standard 3-wire communication is selected. SERIAL PERIPHERAL INTERFACE (SPI) The serial peripheral interface (SPI) is a synchronous bus for address and data transfer and is used when interfacing with the SPI bus on specific Motorola microcontrollers such as the 68HC05C4 and the 68HC11A8. The SPI mode of serial communication is selected by tying the SERMODE pin to VCC. Four pins are used for the SPI. The four pins are the SDO (serial data out), SDI (serial data in), CE (chip enable), and SCLK (serial clock). The DS1306 is the slave device in an SPI application, with the microcontroller being the master. The SDI and SDO pins are the serial data input and output pins for the DS1306, respectively. The CE input is used to initiate and terminate a data transfer. The SCLK pin is used to synchronize data movement between the master (microcontroller) and the slave (DS1306) devices. The shift clock (SCLK), which is generated by the microcontroller, is active only during address and data transfer to any device on the SPI bus. The inactive clock polarity is programmable in some microcontrollers. The DS1306 determines on the clock polarity by sampling SCLK when CE becomes active. Therefore either SCLK polarity can be accommodated. Input data (SDI) is latched on the internal strobe edge and output data (SDO) is shifted out on the shift edge (Figure 5). There is one clock for each bit transferred. Address and data bits are transferred in groups of eight. Figure 5. SERIAL CLOCK AS A FUNCTION OF MICROCONTROLLER CLOCK POLARITY (CPOL) CE CPOL = 1 SCLK SHIFT DATA OUT (READ) DATA LATCH (WRITE) SHIFT DATA OUT (READ) DATA LATCH (WRITE) CPOL = 0 SCLK NOTE 1: CPHA BIT POLARITY (IF APPLICABLE) MAY NEED TO BE SET ACCORDINGLY. NOTE 2: CPOL IS A BIT THAT IS SET IN THE MICROCONTROLLER’S CONTROL REGISTER. NOTE 3: SDO REMAINS AT HIGH-Z UNTIL 8 BITS OF DATA ARE READY TO BE SHIFTED OUT DURING A READ. 11 of 21 DS1306 ADDRESS AND DATA BYTES Address and data bytes are shifted MSB first into the serial data input (SDI) and out of the serial data output (SDO). Any transfer requires the address of the byte to specify a write or read to either a RTC or RAM location, followed by one or more bytes of data. Data is transferred out of the SDO for a read operation and into the SDI for a write operation (Figures 6 and 7). Figure 6. SPI SINGLE-BYTE WRITE * SCLK CAN BE EITHER POLARITY. Figure 7. SPI SINGLE-BYTE READ * SCLK CAN BE EITHER POLARITY. The address byte is always the first byte entered after CE is driven high. The most significant bit (A7) of this byte determines if a read or write takes place. If A7 is 0, one or more read cycles occur. If A7 is 1, one or more write cycles occur. Data transfers can occur one byte at a time or in multiple-byte burst mode. After CE is driven high an address is written to the DS1306. After the address, 1 or more data bytes can be written or read. For a single-byte transfer, one byte is read or written and then CE is driven low. For a multiple-byte transfer, however, multiple bytes can be read or written to the DS1306 after the address has been written. Each read or write cycle causes the RTC register or RAM address to automatically increment. Incrementing continues until the device is disabled. When the RTC is selected, the address wraps to 00h after incrementing to 1Fh (during a read) and wraps to 80h after incrementing to 9Fh (during a write). When the RAM is selected, the address wraps to 20h after incrementing to 7Fh (during a read) and wraps to A0h after incrementing to FFh (during a write). 12 of 21 DS1306 Figure 8. SPI MULTIPLE-BYTE BURST TRANSFER READING AND WRITING IN BURST MODE Burst mode is similar to a single-byte read or write, except that CE is kept high and additional SCLK cycles are sent until the end of the burst. The clock registers and the user RAM may be read or written in burst mode. When accessing the clock registers in burst mode, the address pointer will wrap around after reaching 1Fh (9Fh for writes). When accessing the user RAM in burst mode, the address pointer wraps around after reaching 7Fh (FFh for writes). 3-WIRE INTERFACE The 3-wire interface mode operates similar to the SPI mode. However, in 3-wire mode there is one I/O instead of separate data in and data out signals. The 3-wire interface consists of the I/O (SDI and SDO pins tied together), CE, and SCLK pins. In 3-wire mode, each byte is shifted in LSB first, unlike SPI mode, where each byte is shifted in MSB first. As is the case with the SPI mode, an address byte is written to the device followed by a single data byte or multiple data bytes. Figure 9 illustrates a read and write cycle. In 3-wire mode, data is input on the rising edge of SCLK and output on the falling edge of SCLK. 13 of 21 DS1306 Figure 9. 3-WIRE SINGLE BYTE TRANSFER SINGLE-BYTE READ CE SCLK I/O* A0 A1 A2 A3 A4 A5 A6 0 D0 D1 D2 D3 D4 D5 D6 D7 SINGLE-BYTE WRITE CE SCLK I/O* A0 A1 A2 A3 A4 A5 A6 1 D0 D1 D2 D3 D4 D5 D6 D7 NOTE: IN BURST MODE, CE IS KEPT HIGH AND ADDITIONAL SCLK CYCLES ARE SENT UNTIL THE END OF THE BURST. *I/O IS SDI AND SDO TIED TOGETHER. 14 of 21 DS1306 ABSOLUTE MAXIMUM RATINGS Voltage Range on Any Pin Relative to Ground……………………………………………..-0.5V to +7.0V Storage Temperature Range……………………………………………………………….-55°C to +125°C Soldering Temperature.……………………………….See IPC/JEDEC Standard J-STD-020 Specification This is a stress rating only and functional operation of the device at these or any other conditions beyond those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time can affect reliability. OPERATING RANGE RANGE Commercial TEMP RANGE 0°C to +70°C VCC (V) 2.0 to 5.5 VCC1 or VCC2 Industrial -40°C to +85°C 2.0 to 5.5 VCC1 or VCC2 RECOMMENDED DC OPERATING CONDITIONS (TA = Over the operating range, unless otherwise specified.) PARAMETER Supply Voltage VCC1, VCC2 Logic 1 Input SYMBOL MIN TYP MAX UNITS NOTES 1, 8 VCC1, VCC2 2.0 5.5 V VIH 2.0 V V V VBAT Battery Voltage VBAT 2.0 VCC + 0.3 +0.3 +0.8 5.5 VCCIF Supply Voltage VCCIF 2.0 5.5 Logic 0 Input VIL VCC = 2.0V VCC = 5V 15 of 21 -0.3 V 10 DS1306 DC ELECTRICAL CHARACTERISTICS (TA = Over the operating range, unless otherwise specified.) PARAMETER Input Leakage Output Leakage IOL = 1.5mA Logic 0 Output IOL = 4.0mA IOH = -0.4mA Logic 1 Output IOH = -1.0mA Logic 1 Output Current (INT1 pin) IOH, INT1 VCC1 Active Supply Current ICC1A VCC1 Timekeeping Current ICC1T VCC2 Active Supply Current ICC2A VCC2 Timekeeping Current ICC2T Battery Timekeeping Current Battery Timekeeping Current (IND) IBAT VBAT = 3V IBAT VBAT = 3V VCC Trip Point SYMBOL MIN -100 -1 ILI ILO VOL VOH VCC = 2.0 VCC = 5V VCCIF = 2.0V VCCIF = 5V (VCC2, VBAT) -0.3V VCC1 = 2.0V VCC1 = 5V VCC1 = 2.0V VCC1 = 5V VCC2 = 2.0V VCC2 = 5V VCC2 = 2.0V VCC2 = 5V TYP UNITS mA mA V -100 mA 0.425 1.28 25.3 81 0.4 1.2 0.4 1 NOTES V 1.6 2.4 VBAT 50 VCCTP MAX +500 +1 0.4 0.4 mA 2, 7 mA 1, 7 mA 2, 8 mA 1, 8 550 nA 9 800 nA 9 VBAT + 200 mV Trickle Charge Resistors R1 R2 R3 2 4 8 kW Trickle Charger Diode Voltage Drop VTD 0.7 V CAPACITANCE (TA = +25°C) PARAMETER Input Capacitance Output Capacitance Crystal Capacitance SYMBOL CI CO CX 16 of 21 MIN TYP 10 15 6 MAX UNITS pF pF pF NOTES DS1306 3-WIRE AC ELECTRICAL CHARACTERISTICS (TA = Over the operating range, unless otherwise specified.) (Figure 10 and Figure 11) PARAMETER Data to CLK Setup CLK to Data Hold CLK to Data Delay CLK Low Time CLK High Time CLK Frequency CLK Rise and Fall CE to CLK Setup CLK to CE Hold CE Inactive Time CE to Output High-Z SCLK to Output High-Z SYMBOL VCC = 2.0V tDC VCC = 5V VCC = 2.0V tCDH VCC = 5V VCC = 2.0V tCDD VCC = 5V VCC = 2.0V tCL VCC = 5V VCC = 2.0V tCH VCC = 5V VCC = 2.0V tCLK VCC = 5V VCC = 2.0V tR, t F VCC = 5V VCC = 2.0V tCC VCC = 5V VCC = 2.0V tCCH VCC = 5V VCC = 2.0V tCWH VCC = 5V VCC = 2.0V tCDZ VCC = 5V VCC = 2.0V tCCZ VCC = 5V 17 of 21 MIN 200 50 280 70 TYP MAX 800 200 1000 250 1000 250 DC 0.6 2.0 2000 500 4 1 240 60 4 1 280 70 280 70 UNITS NOTES ns 3, 4 ns 3, 4 ns 3, 4, 5 ns 4 ns 4 MHz 4 ns ms 4 ns 4 ms 4 ns 3, 4 ns 3, 4 DS1306 Figure 10. TIMING DIAGRAM: 3-WIRE READ DATA TRANSFER * I/O IS SDI AND SDO TIED TOGETHER. Figure 11. TIMING DIAGRAM: 3-WIRE WRITE DATA TRANSFER * I/O IS SDI AND SDO TIED TOGETHER. 18 of 21 DS1306 SPI AC ELECTRICAL CHARACTERISTICS (TA = Over the operating range, unless otherwise specified.) PARAMETER Data to CLK Setup CLK to Data Hold CLK to Data Delay CLK Low Time CLK High Time CLK Frequency CLK Rise and Fall CE to CLK Setup CLK to CE Hold CE Inactive Time CE to Output High-Z SYMBOL VCC = 2.0V tDC VCC = 5V VCC = 2.0V tCDH VCC = 5V VCC = 2.0V tCDD VCC = 5V VCC = 2.0V tCL VCC = 5V VCC = 2.0V tCH VCC = 5V VCC = 2.0V tCLK VCC = 5V VCC = 2.0V tR, t F VCC = 5V VCC = 2.0V tCC VCC = 5V VCC = 2.0V tCCH VCC = 5V VCC = 2.0V tCWH VCC = 5V VCC = 2.0V tCDZ VCC = 5V 19 of 21 MIN 200 50 280 70 TYP MAX 800 200 1000 250 1000 250 DC 0.6 2.0 2000 500 4 1 240 60 4 1 280 70 UNITS NOTES ns 3, 4 ns 3, 4 ns 3, 4, 5 ns 4 ns 4 MHz 4 ns ms 4 ns 4 ms 4 ns 3, 4 DS1306 Figure 12. TIMING DIAGRAM: SPI READ DATA TRANSFER * SCLK CAN BE EITHER POLARITY, TIMING SHOWN FOR CPOL = 1. Figure 13. TIMING DIAGRAM: SPI WRITE DATA TRANSFER * SCLK CAN BE EITHER POLARITY, TIMING SHOWN FOR CPOL = 1. 20 of 21 DS1306 NOTES: 1) ICC1T and ICC2T are specified with CE set to a logic 0. 2) ICC1A and ICC2A are specified with CE = VCC, SCLK = 2MHz at VCC = 5V; SCLK = 500kHz at VCC = 2.0V, VIL = 0V, VIH = VCC. 3) Measured at VIH = 2.0V or VIL = 0.8V and 10ms maximum rise and fall time. 4) Measured with 50pF load. 5) Measured at VOH = 2.4V or VOL = 0.4V. 6) VCC = VCC1, when VCC1 > VCC2 + 0.2V (typical); VCC = VCC2, when VCC2 > VCC1. 7) VCC2 = 0V. 8) VCC1 = 0V. 9) VCC1 < VBAT. 10) VCCIF must be less than or equal to the largest of VCC1, VCC2, and VBAT. 21 of 21 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. 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