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DS1302 Trickle Charge Timekeeping Chip
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 31-byte, battery-backed, nonvolatile (NV) RAM for data storage Serial I/O for minimum pin count 2.0V to 5.5V full operation Uses less than 300nA at 2.0V Burst mode for reading/writing successive addresses in clock/RAM 8-pin DIP or optional 8-pin SOICs for surface mount Simple 3-wire interface TTL-compatible (VCC = 5V) Optional industrial temperature range: -40C to +85C DS1202 compatible Underwriters Laboratory (UL) recognized
PIN ASSIGNMENT
VCC2 X1 X2 GND 1 2 3 4 8 7 6 5 VCC1 SCLK I/O RST

DS1302 8-Pin DIP (300-mil)
VCC2 X1 X2 GND
1 2 3 4
8 7 6 5
VCC1 SCLK I/O RST
DS1302 8-Pin SOIC (200-mil) DS1302 8-Pin SOIC (150-mil)
VCC2 NC X1 NC X2 NC NC GND 1 2 3 4 5 6 7 8 16 15 14 13 12 11 10 9 VCC1 NC SCLK NC I/O NC NC
RST
ORDERING INFORMATION
DS1302 DS1302N DS1302S DS1302SN DS1302Z DS1302ZN DS1302S-16 DS1302SN-16 8-Pin DIP (300-mil) 8-Pin DIP (Industrial) 8-Pin SOIC (200-mil) 8-Pin SOIC (Industrial) 8-Pin SOIC (150-mil) 8-Pin SOIC (Industrial) 16-Pin SOIC (300-mil) 16-Pin SOIC (Industrial)
DS1302 16-Pin SOIC (300-mil)
PIN DESCRIPTION
X1, X2 GND
RST
I/O SCLK VCC1, VCC2
- 32.768kHz Crystal Pins - Ground - Reset - Data Input/Output - Serial Clock - Power Supply Pins
DESCRIPTION
The DS1302 Trickle Charge Timekeeping Chip contains an RTC/calendar and 31 bytes of static RAM. It communicates with a microprocessor via a simple serial interface. The RTC/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 an AM/PM indicator.
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Interfacing the DS1302 with a microprocessor is simplified by using synchronous serial communication. Only three wires are required to communicate with the clock/RAM: 1) RST (reset), 2) I/O (data line), and 3) SCLK (serial clock). Data can be transferred to and from the clock/RAM 1 byte at a time or in a burst of up to 31 bytes. The DS1302 is designed to operate on very low power and retain data and clock information on less than 1 microwatt. The DS1302 is the successor to the DS1202. In addition to the basic timekeeping functions of the DS1202, the DS1302 has the additional features of dual-power pins for primary and back-up power supplies, programmable trickle charger for VCC1, and seven additional bytes of scratchpad memory.
TYPICAL OPERATING CIRCUIT
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OPERATION
The main elements of the serial timekeeper (i.e., shift register, control logic, oscillator, RTC, and RAM) are shown in Figure 1.
DS1302 BLOCK DIAGRAM Figure 1
SIGNAL DESCRIPTIONS
VCC1 - VCC1 provides low-power operation in single supply and battery-operated systems as well as lowpower battery backup. In systems using the trickle charger, the rechargeable energy source is connected to this pin. UL recognized to ensure against reverse charging current when used in conjunction with a lithium battery. See "Conditions of Acceptability" at http://www.maxim-ic.com/TechSupport/QA/ntrl.htm. VCC2 - VCC2 is the primary power supply pin in a dual-supply configuration. VCC1 is connected to a backup source to maintain the time and date in the absence of primary power. The DS1302 will operate from the larger of VCC1 or VCC2. When VCC2 is greater than VCC1 + 0.2V, VCC2 will power the DS1302. When VCC2 is less than VCC1, VCC1 will power the DS1302. SCLK (Serial Clock Input) - SCLK is used to synchronize data movement on the serial interface. This pin has a 40k internal pull-down resistor. I/O (Data Input/Output) - The I/O pin is the bi-directional data pin for the 3-wire interface. This pin has a 40k internal pull-down resistor. RST (Reset) - The reset signal must be asserted high during a read or a write. This pin has a 40k internal pull-down resistor. X1, X2 - Connections for a 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, please consult Application Note 58, "Crystal Considerations
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with Dallas Real-Time Clocks." The DS1302 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.
RECOMMENDED LAYOUT FOR CRYSTAL
CLOCK ACCURACY
The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match between the capactive load of the oscillator circuit and the capacitive load for which the crystal was trimmed. Additional error will be added by crystal frequency drift caused by temperature shifts. External circuit noise coupled into the oscillator circuit may result in the clock running fast. See Application Note 58, "Crystal Considerations with Dallas Real-Time Clocks" for detailed information.
COMMAND BYTE
The command byte is shown in Figure 2. Each data transfer is initiated by a command byte. The MSB (Bit 7) must be a logic 1. If it is 0, writes to the DS1302 will be disabled. Bit 6 specifies clock/calendar data if logic 0 or RAM data if logic 1. Bits 1 through 5 specify the designated registers to be input or output, and the LSB (bit 0) specifies a write operation (input) if logic 0 or read operation (output) if logic 1. The command byte is always input starting with the LSB (bit 0).
ADDRESS/COMMAND BYTE Figure 2
RESET AND CLOCK CONTROL
All data transfers are initiated by driving the RST input high. The RST input serves two functions. First, RST turns on the control logic, which allows access to the shift register for the address/command sequence. Second, the RST signal provides a method of terminating either single byte or multiple byte data transfer. A clock cycle is a sequence of a falling edge followed by a rising edge. For data inputs, data must be valid during the rising edge of the clock and data bits are output on the falling edge of clock. If the RST input is low all data transfer terminates and the I/O pin goes to a high impedance state. Data transfer is illustrated in Figure 3. At power-up, RST must be a logic 0 until VCC > 2.0V. Also SCLK must be at a logic 0 when RST is driven to a logic 1 state.
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DATA INPUT
Following the eight SCLK cycles that input a write command byte, a data byte is input on the rising edge of the next eight SCLK cycles. Additional SCLK cycles are ignored should they inadvertently occur. Data is input starting with bit 0.
DATA OUTPUT
Following the eight SCLK cycles that input a read command byte, a data byte is output on the falling edge of the next eight SCLK cycles. Note that the first data bit to be transmitted occurs on the first falling edge after the last bit of the command byte is written. Additional SCLK cycles retransmit the data bytes should they inadvertently occur so long as RST remains high. This operation permits continuous burst mode read capability. Also, the I/O pin is tri-stated upon each rising edge of SCLK. Data is output starting with bit 0.
BURST MODE
Burst mode may be specified for either the clock/calendar or the RAM registers by addressing location 31 decimal (address/command bits 1 through 5 = logic 1). As before, bit 6 specifies clock or RAM and bit 0 specifies read or write. There is no data storage capacity at locations 9 through 31 in the Clock/Calendar Registers or location 31 in the RAM registers. Reads or writes in burst mode start with bit 0 of address 0. When writing to the clock registers in the burst mode, the first eight registers must be written in order for the data to be transferred. However, when writing to RAM in burst mode it is not necessary to write all 31 bytes for the data to transfer. Each byte that is written to will be transferred to RAM regardless of whether all 31 bytes are written or not.
CLOCK/CALENDAR
The clock/calendar is contained in seven write/read registers as shown in Figure 4. Data contained in the clock/ calendar registers is in binary coded decimal format (BCD).
CLOCK HALT FLAG
Bit 7 of the seconds register is defined as the clock halt flag. When this bit is set to logic 1, the clock oscillator is stopped and the DS1302 is placed into a low-power standby mode with a current drain of less than 100 nanoamps. When this bit is written to logic 0, the clock will start. The initial power on state is not defined.
AM-PM/12-24 MODE
Bit 7 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 (20-23 hours).
WRITE PROTECT BIT
Bit 7 of the control register is the write-protect bit. The first seven bits (bits 0-6) are forced to 0 and will always read a 0 when read. Before any write operation to the clock or RAM, bit 7 must be 0. When high, the write protect bit prevents a write operation to any other register. The initial power on state is not defined. Therefore the WP bit should be cleared before attempting to write to the device.
TRICKLE CHARGE REGISTER
This register controls the trickle charge characteristics of the DS1302. The simplified schematic of Figure 5 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 will enable the trickle charger. All other patterns will disable the trickle charger. The
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DS1302 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 VCC2 and VCC1. If DS is 01, one diode is selected or if DS is 10, two diodes are selected. If DS is 00 or 11, the trickle charger is disabled independently of TCS. The RS bits (bits 0-1) select the resistor that is connected between VCC2 and VCC1. The resistor selected by the resistor select (RS) bits is as follows: RS Bits 00 01 10 11 Resistor None R1 R2 R3 Typical Value None 2k 4k 8k
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 VCC2 and a super cap is connected to VCC1. Also assume that the trickle charger has been enabled with one diode and resistor R1 between VCC2 and VCC1. The maximum current IMAX would, therefore, be calculated as follows: IMAX = (5.0V - diode drop)/R1 (5.0V - 0.7V) / 2k 2.2mA As the super cap charges, the voltage drop between VCC1 and VCC2 will decrease and, therefore, the charge current will decrease.
CLOCK/CALENDAR BURST MODE
The clock/calendar command byte specifies burst mode operation. In this mode the first eight clock/calendar registers can be consecutively read or written (See Figure 4) starting with bit 0 of address 0. If the write protect bit is set high when a write clock/calendar burst mode is specified, no data transfer will occur to any of the eight clock/calendar registers (this includes the control register). The trickle charger is not accessible in burst mode. At the beginning of a clock burst read, the current time is transferred to a second set of registers. The time information is read from these secondary registers, while the clock may continue to run. This eliminates the need to re-read the registers in case of an update of the main registers during a read.
RAM
The static RAM is 31 x 8 bytes addressed consecutively in the RAM address space.
RAM BURST MODE
The RAM command byte specifies burst mode operation. In this mode, the 31 RAM registers can be consecutively read or written (See Figure 4) starting with bit 0 of address 0.
REGISTER SUMMARY
A register data format summary is shown in Figure 4.
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DATA TRANSFER SUMMARY Figure 3
SINGLE BYTE READ RST SCLK I/O SINGLE BYTE WRITE RST SCLK I/O
R/ W A0 A1 A2 A3 A4 R/C 1 D0 D1 D2 D3 D4 D5 D6 D7 R/ W A0 A1 A2 A3 A4 R/C 1
In burst mode, RST is kept high and additional SCLK cycles are sent until the end of the burst.
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REGISTER ADDRESS/DEFINITION Figure 4
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DS1302 PROGRAMMABLE TRICKLE CHARGER Figure 5
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ABSOLUTE MAXIMUM RATINGS*
Voltage on Any Pin Relative to Ground Storage Temperature Soldering Temperature -0.5V to +7.0V -55C to +125C 260C for 10 seconds (DIP) See IPC/JEDEC Standard J-STD-020A for Surface Mount Devices
* This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. Range Commercial Industrial Temperature 0C to 70C -40C to +85C VCC 2.0V to 5.5V VCC1 or VCC2 2.0V to 5.5V VCC1 or VCC2
RECOMMENDED DC OPERATING CONDITIONS (Over the operating range*)
PARAMETER Supply Voltage VCC1, VCC2 Logic 1 Input Logic 0 Input *Unless otherwise specified. SYMBOL VCC1, VCC2 VIH VIL VCC = 2.0V VCC = 5V MIN TYP 2.0 2.0 -0.3 -0.3 MAX 5.5 VCC + 0.3 +0.3 +0.8 UNITS V V V NOTES 8
DC ELECTRICAL CHARACTERISTICS (Over the operating range*)
PARAMETER Input Leakage I/O Leakage Logic 1 Output IOH = -0.4mA IOH = -1.0mA Logic 0 Output IOL = 1.5mA IOL = 4.0mA Active Supply Current Timekeeping Current (OSC On) Standby Current (OSC Off) Active Supply Current Timekeeping Current (OSC On) Standby Current (OSC Off) SYMBOL ILI ILO VOH VOL ICC1A ICC1T ICC1S ICC2A ICC2T ICC2S VCC = 2.0V VCC = 5V VCC = 2.0V VCC = 5V VCC1 = 2.0V VCC1 = 5V VCC1 = 2.0V VCC1 = 5V VCC1 = 2.0V VCC1 = 5V IND VCC2 = 2.0V VCC2 = 5V VCC2 = 2.0V VCC2 = 5V VCC2 = 2.0V VCC2 = 5V
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MIN TYP 1.6 2.4
MAX +500 +500 0.4 0.4 0.4 1.2 0.3 1 100 100 200 0.425 1.28 25.3 81 25 80
UNITS NOTES mA 3 mA 3 V V mA mA nA mA mA mA 2,9 1,9 7,9,11 2,10 1,10 7,10
DS1302
Trickle Charge Resistors Trickle Charge Diode Voltage Drop *Unless otherwise specified.
R1 R2 R3 VTD
2 4 8 0.7
k k k V
CAPACITANCE
PARAMETER Input Capacitance I/O Capacitance Crystal Capacitance SYMBOL CI CI/O CX MIN TYP 10 15 6 MAX
(TA = 25C)
UNITS pF pF pF NOTES
AC ELECTRICAL CHARACTERISTICS (Over the operating range*)
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
RST to CLK Setup
CLK to RST Hold
RST Inactive Time RST to I/O High-Z
SCLK to I/O High-Z *Unless otherwise specified.
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
MIN TYP 200 50 280 70 1000 250 1000 250 DC 4 1 240 60 4 1
MAX
UNITS NOTES ns ns 4 4 4,5,6 4 4 4 4 4 4 4 4 4
800 200
ns ns ns
0.5 2.0 2000 500
MHz ns ms ns ms
280 70 280 70
ns ns
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TIMING DIAGRAM: READ DATA TRANSFER Figure 5
TIMING DIAGRAM: WRITE DATA TRANSFER Figure 6
NOTES:
1. ICC1T and ICC2T are specified with I/O open, RST set to a logic 0, and clock halt flag = 0 (oscillator enabled). 2. ICC1A and ICC2A are specified with the I/O pin open, RST high, SCLK=2MHz at VCC = 5V; SCLK = 500kHz, VCC = 2.0V, and clock halt flag = 0 (oscillator enabled). 3. RST , SCLK, and I/O all have 40k pull-down resistors to ground. 4. Measured at VIH = 2.0V or VIL = 0.8V and 10ns maximum rise and fall time. 5. Measured at VOH = 2.4V or VOL = 0.4V. 6. Load capacitance = 50pF. 7. ICC1S and ICC2S are specified with RST , I/O, and SCLK open. The clock halt flag must be set to logic one (oscillator disabled). 8. VCC = VCC2, when VCC2 > VCC1 + 0.2V; VCC = VCC1, when VCC1 > VCC2. 9. VCC2 = 0V. 10. VCC1 = 0V. 11. Typical values are at 25C.
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DS1302 SERIAL TIMEKEEPER 8-PIN DIP (300-MIL)
PKG DIM A IN. MM B IN. MM C IN. MM D IN. MM E IN. MM F IN. MM G IN. MM H IN. MM J IN. MM K IN. MM 8-PIN MIN MAX 0.360 0.400 9.14 10.16 0.240 0.260 6.10 6.60 0.120 0.140 3.05 3.56 0.300 0.325 7.62 8.26 0.015 0.040 0.38 1.02 0.120 0.140 3.04 3.56 0.090 0.110 2.29 2.79 0.320 0.370 8.13 9.40 0.008 0.012 0.20 0.30 0.015 0.021 0.38 0.53
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DS1302S SERIAL TIMEKEEPER 8-PIN SOIC (150-MIL AND 200-MIL)
PKG DIM A IN. MM B IN. MM C IN. MM E IN. MM F IN. MM G IN. MM H IN. MM J IN. MM K IN. MM L IN. MM phi 8-PIN 8-PIN (150-MIL) (200-MIL) MIN MAX MIN MAX 0.188 0.196 0.203 0.213 4.78 4.98 5.16 5.41 0.150 0.158 0.203 0.213 3.81 4.01 5.16 5.41 0.048 0.062 0.070 0.074 1.22 1.57 1.78 1.88 0.004 0.010 0.004 0.010 0.10 0.25 0.10 0.25 0.053 0.069 0.074 0.084 1.35 1.75 1.88 2.13 0.050 BSC 1.27 BSC 0.230 0.244 0.302 0.318 5.84 6.20 7.67 8.08 0.007 0.011 0.006 0.010 0.18 0.28 0.15 0.25 0.012 0.020 0.013 0.020 0.30 0.51 0.33 0.51 0.016 0.050 0.019 0.030 0.41 1.27 0.48 0.76 0 8 0 8
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DS1302S SERIAL TIMEKEEPER 16-PIN SOIC
A B C E F G H J K L phi
PKG DIM IN MM IN MM IN MM IN MM IN MM IN MM IN MM IN MM IN MM IN MM
16-PIN MIN MAX 0.398 0.412 10.11 10.46 0.290 0.300 7.37 7.62 0.089 0.095 2.26 2.41 0.004 0.012 0.102 0.30 0.004 0.105 2.39 2.67 0.050 BSC 1.27 BSC 0.398 0.416 10.11 10.57 0.009 0.013 0.229 0.33 0.013 0.020 0.33 0.51 0.016 0.040 0.40 1.02 0 8
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