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| DS1742 Y2KC Nonvolatile Timekeeping RAM www.dalsemi.com FEATURES Integrated NV SRAM, real time clock, crystal, power-fail control circuit and lithium energy source Clock registers are accessed identical to the static RAM. These registers are resident in the eight top RAM locations Century byte register Totally nonvolatile with over 10 years of operation in the absence of power BCD coded century, year, month, date, day, hours, minutes, and seconds with automatic leap year compensation valid up to the year 2100 Battery voltage level indicator flag Power-fail write protection allows for 10% VCC power supply tolerance Lithium energy source is electrically disconnected to retain freshness until power is applied for the first time Standard JEDEC bytewide 2k x 8 static RAM pinout Quartz accuracy 1 minute a month @ 25C, factory calibrated PIN ASSIGNMENT A7 A6 A5 A4 A3 A2 A1 A0 DQ0 DQ1 DQ2 GND 1 2 3 4 5 6 7 8 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 VCC A8 A9 WE OE A10 CE DQ7 DQ6 DQ5 DQ4 DQ3 PIN DESCRIPTION A0-A10 CE OE WE VCC GND DQ0-DQ7 - Address Inputs - Chip Enable - Output Enable - Write Enable - Power Supply Input - Ground - Data Input/Outputs ORDERING INFORMATION DS1742-XXX (5V) -70 -100 70 ns access 100 ns access DS1742W-XXX (3.3V) -120 120 ns access -150 150 ns access DESCRIPTION The DS1742 is a full function, year 2000-compliant (Y2KC), real-time clock/calendar (RTC) and 2k x 8 non-volatile static RAM. User access to all registers within the DS1742 is accomplished with a bytewide interface as shown in Figure 1. The Real Time Clock (RTC) information and control bits reside in the eight uppermost RAM locations. The RTC registers contain century, year, month, date, day, hours, minutes, and seconds data in 24-hour BCD format. Corrections for the day of the month and leap year are made automatically. 1 of 12 091800 DS1742 The RTC clock registers are double-buffered to avoid access of incorrect data that can occur during clock update cycles. The double buffered system also prevents time loss as the timekeeping countdown continues unabated by access to time register data. The DS1742 also contains its own power-fail circuitry, which deselects the device when the VCC supply is in an out of tolerance condition. This feature prevents loss of data from unpredictable system operation brought on by low VCC as errant access and update cycles are avoided. CLOCK OPERATIONS-READING THE CLOCK While the double-buffered register structure reduces the chance of reading incorrect data, internal updates to the DS1742 clock registers should be halted before clock data is read to prevent reading of data in transition. However, halting the internal clock register updating process does not affect clock accuracy. Updating is halted when a 1 is written into the read bit, bit 6 of the century register, see Table 2. As long as a 1 remains in that position, updating is halted. After a halt is issued, the registers reflect the count, that is day, date, and time that was current at the moment the halt command was issued. However, the internal clock registers of the double-buffered system continue to update so that the clock accuracy is not affected by the access of data. All of the DS1742 registers are updated simultaneously after the internal clock register updating process has been re-enabled. Updating is within a second after the read bit is written to 0. The READ bit must be a zero for a minimum of 500 s to ensure the external registers will be updated. DS1742 BLOCK DIAGRAM Figure 1 DS1742 TRUTH TABLE Table 1 VCC VCC>VPF VSO X X VIL VIH X X X VIL VIH VIH X X MODE DESELECT WRITE READ READ DESELECT DESELECT DQ HIGH-Z DATA IN DATA OUT HIGH-Z HIGH-Z HIGH-Z POWER STANDBY ACTIVE ACTIVE ACTIVE CMOS STANDBY DATA RETENTION MODE SETTING THE CLOCK As shown in Table 2, bit 7 of the century register is the write bit. Setting the write bit to a 1, like the read bit, halts updates to the DS1742 registers. The user can then load them with the correct day, date and time data in 24-hour BCD format. Resetting the write bit to a 0 then transfers those values to the actual clock counters and allows normal operation to resume. 2 of 12 DS1742 STOPPING AND STARTING THE CLOCK OSCILLATOR The clock oscillator may be stopped at any time. To increase the shelf life, the oscillator can be turned off to minimize current drain from the battery. The OSC bit is the MSB (bit 7) of the seconds registers, see Table 2. Setting it to a 1 stops the oscillator. FREQUENCY TEST BIT As shown in Table 2, bit 6 of the day byte is the frequency test bit. When the frequency test bit is set to logic 1 and the oscillator is running, the LSB of the seconds register will toggle at 512 Hz. When the seconds register is being read, the DQ0 line will toggle at the 512 Hz frequency as long as conditions for access remain valid (i.e., CE low, OE low, WE high, and address for seconds register remain valid and stable). CLOCK ACCURACY The DS1742 is guaranteed to keep time accuracy to within 1 minute per month at 25C. The RTC is calibrated at the factory by Dallas Semiconductor using nonvolatile tuning elements. The DS1742 does not require additional calibration. For this reason, methods of field clock calibration are not available and not necessary. Clock accuracy is also effected by the electrical environment and caution should be taken to place the RTC in the lowest level EMI section of the PCB layout. For additional information please see application note 58. DS1742 REGISTER MAP Table 2 ADDRESS DATA B7 B6 B5 B4 B3 B2 B1 B0 FUNCTION/RANGE 7FF 7FE 7FD 7FC 7FB 7FA 7F9 7F8 X X BF X X OSC W R X X 10 Year X X 10 MINUTES 10 SECONDS 10 CENTURY 10 Mo 10 Date X X 10 HOUR YEAR MONTH DATE DAY HOUR MINUTES SECONDS CENTURY YEAR MONTH DATE DAY HOUR MINUTES SECONDS CONTROL 00-99 01-12 01-31 01-07 00-23 00-59 00-59 00-39 FT X OSC = STOP BIT W = WRITE BIT R = READ BIT X = SEE NOTE BELOW FT = FREQUENCY TEST BF = BATTERY FLAG NOTE: All indicated "X" bits are not dedicated to any particular function and can be used as normal RAM bits. RETRIEVING DATA FROM RAM OR CLOCK The DS1742 is in the read mode whenever OE (output enable) is low, WE (write enable) is high, and CE (chip enable) is low. The device architecture allows ripplethrough access to any of the address locations in the NV SRAM. Valid data will be available at the DQ pins within tAA after the last address input is stable, providing that the CE , and OE access times and states are satisfied. If CE , or OE access times and states are not met, valid data will be available at the latter of chip enable access (tCEA) or at output enable access time (tOEA). The state of the data input/output pins (DQ) is controlled by CE , and OE . If the outputs are activated before tAA, the data lines are driven to an intermediate state until tAA. If the 3 of 12 DS1742 address inputs are changed while CE , and OE remain valid, output data will remain valid for output data hold time (tOH) but will then go indeterminate until the next address access. WRITING DATA TO RAM OR CLOCK The DS1742 is in the write mode whenever WE , and CE are in their active state. The start of a write is referenced to the latter occurring transition of WE , on CE . The addresses must be held valid throughout the cycle. CE , or WE must return inactive for a minimum of tWR prior to the initiation of another read or write cycle. Data in must be valid tDS prior to the end of write and remain valid for tDH afterward. In a typical application, the OE signal will be high during a write cycle. However, OE can be active provided that care is taken with the data bus to avoid bus contention. If OE is low prior to WE transitioning low the data bus can become active with read data defined by the address inputs. A low transition on WE will then disable the outputs tWEZ after WE goes active. DATA RETENTION MODE The 5-volt device is fully accessible and data can be written or read only when VCC is greater than VPF. However, when VCC is below the power fail point, VPF, (point at which write protection occurs) the internal clock registers and SRAM are blocked from any access. At this time the power fail reset output signal ( RST ) is driven active and will remain active until VCC returns to nominal levels. When VCC falls below the battery switch point VSO (battery supply level), device power is switched from the VCC pin to the backup battery. RTC operation and SRAM data are maintained from the battery until VCC is returned to nominal levels. The 3.3 volt device is fully accessible and data can be written or read only when VCC is greater than VPF. When VCC falls below the power fail point, VPF, access to the device is inhibited. At this time the power fail reset output signal ( RST ) is driven active and will remain active until VCC returns to nominal levels. If VPF is less than Vso, the device power is switched from VCC to the backup supply (VBAT) when VCC drops below VPF. If VPF is greater than Vso, the device power is switched from VCC to the backup supply (VBAT) when VCC drops below Vso. RTC operation and SRAM data are maintained from the battery until VCC is returned to nominal levels. The RST signal is an open drain output and requires a pull up. Except for the RST , all control, data, and address signals must be powered down when VCC is powered down. BATTERY LONGEVITY The DS1742 has a lithium power source that is designed to provide energy for clock activity, and clock and RAM data retention when the VCC supply is not present. The capability of this internal power supply is sufficient to power the DS1742 continuously for the life of the equipment in which it is installed. For specification purposes, the life expectancy is 10 years at 25C with the internal clock oscillator running in the absence of VCC power. Each DS1742 is shipped from Dallas Semiconductor with its lithium energy source disconnected, guaranteeing full energy capacity. When VCC is first applied at a level greater than VPF, the lithium energy source is enabled for battery backup operation. Actual life expectancy of the DS1742 will be much longer than 10 years since no lithium battery energy is consumed when VCC is present. BATTERY MONITOR The DS1742 constantly monitors the battery voltage of the internal battery. The Battery Flag bit (bit 7) of the day register is used to indicate the voltage level range of the battery. This bit is not writable and should always be a 1 when read. If a 0 is ever present, an exhausted lithium energy source is indicated and both the contents of the RTC and RAM are questionable. 4 of 12 DS1742 ABSOLUTE MAXIMUM RATINGS* Voltage on Any Pin Relative to Ground Operating Temperature Storage Temperature Soldering Temperature -0.3V to +6.0V 0C to 70C -20C to +70C See J-STD-020A Specification (See Note 7) * 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. OPERATING RANGE Range Commercial Temperature 0C to +70C VCC 3.3V 10% or 5V 10% RECOMMENDED DC OPERATING CONDITIONS PARAMETER Logic 1 Voltage All Inputs VCC = 5V 10% VCC = 3.3V 10% Logic 0 Voltage All Inputs VCC = 5V 10% VCC = 3.3V 10% SYMBOL VIH VIH VIL VIL MIN 2.2 2.0 -0.3 -0.3 TYP (Over the Operating Range) MAX VCC +0.3V VCC +0.3V 0.8 0.6 UNITS V V V V NOTES 1 1 1 1 DC ELECTRICAL CHARACTERISTICS (Over the Operating Range; VCC = 5.0V 10%) PARAMETER Active Supply Current TTL Standby Current ( CE =VIH ) CMOS Standby Current ( CE =VCC - 0.2V) Input Leakage Current (any input) Output Leakage Current (any output) Output Logic 1 Voltage (IOUT = -1.0 mA) Output Logic 0 Voltage (IOUT = +2.1 mA) Write Protection Voltage Battery Switch-over Voltage SYMBOL ICC ICC1 ICC2 IIL IOL VOH -1 -1 2.4 MIN TYP 15 1 1 MAX 50 3 3 +1 +1 UNITS mA mA mA A A 1 NOTES 2, 3 2, 3 2, 3 VOL VPF VSO 4.25 VBAT 0.4 4.50 V 1 1 1, 4 5 of 12 DS1742 DC ELECTRICAL CHARACTERISTICS (Over the Operating Range; VCC = 3.3V 10%) PARAMETER Active Supply Current TTL Standby Current ( CE = VIH ) CMOS Standby Current ( CE =VCC - 0.2V) Input Leakage Current (any input) Output Leakage Current (any output) Output Logic 1 Voltage (IOUT = -1.0 mA) Output Logic 0 Voltage (IOUT =2.1 mA) Write Protection Voltage Battery Switch-over Voltage SYMBOL ICC ICC1 ICC2 IIL IOL VOH -1 -1 2.4 MIN TYP 10 0.7 0.7 MAX 30 2 2 +1 +1 UNITS mA mA mA A A 1 NOTES 2, 3 2, 3 2, 3 VOL VPF VSO 2.80 VBAT or VPF 0.4 2.97 V V 1 1 1, 4 READ CYCLE, AC CHARACTERISTICS (Over the Operating Range; VCC = 5.0V 10%) PARAMETER Read Cycle Time Address Access Time to DQ Low-Z CE Access Time CE Data Off time OE to DQ Low-Z OE Access Time OE Data Off Time Output Hold from Address CE SYMBOL tRC tAA tCEL tCEA tCEZ tOEL tOEA tOEZ tOH 70 ns access MIN MAX 70 70 5 70 25 5 35 25 5 100 ns access MIN MAX 100 100 5 100 35 5 55 35 5 UNITS ns ns ns ns ns ns ns ns ns NOTES 6 of 12 DS1742 READ CYCLE, AC CHARACTERISTICS (Over the Operating Range; VCC = 3.3V 10%) PARAMETER Read Cycle Time Address Access Time to DQ Low-Z CE Access Time CE Data Off time OE to DQ Low-Z OE Access Time OE Data Off Time Output Hold from Address CE SYMBOL tRC tAA tCEL tCEA tCEZ tOEL tOEA tOEZ tOH 120 ns access MIN MAX 120 120 5 120 40 5 100 35 5 150 ns access MIN MAX 150 150 5 150 50 5 130 35 5 UNITS ns ns ns ns ns ns ns ns ns NOTES 5 5 5 5 5 5 5 5 5 READ CYCLE TIMING DIAGRAM 7 of 12 DS1742 WRITE CYCLE, AC CHARACTERISTICS (Over the Operating Range; VCC = 5.0V 10%) PARAMETER Write Cycle Time Address Access Time Pulse Width CE Pulse Width Data Setup Time Data Hold time Address Hold Time WE Data Off Time Write Recovery Time WE SYMBOL tWC tAS tWEW tCEW tDS tDH tAH tWEZ tWR 70 ns access MIN MAX 70 0 50 60 30 0 5 25 5 100 ns access MIN MAX 100 0 70 75 40 0 5 35 5 UNITS ns ns ns ns ns ns ns ns ns NOTES WRITE CYCLE, AC CHARACTERISTICS (Over the Operating Range; VCC = 3.3V 10%) PARAMETER Write Cycle Time Address Setup Time Pulse Width CE Pulse Width Data Setup Time Data Hold Time Address Hold Time WE Data Off Time Write Recovery Time WE SYMBOL tWC tAS tWEW tCEW tDS tDH tAH tWEZ tWR 120 ns access MIN MAX 120 0 100 110 80 0 0 40 10 150 ns access MIN MAX 150 0 130 140 90 0 0 50 10 UNITS ns ns ns ns ns ns ns ns ns NOTES 8 of 12 DS1742 WRITE CYCLE TIMING DIAGRAM, WRITE ENABLE CONTROLLED WRITE CYCLE TIMING DIAGRAM, CE CONTROLLED POWER-UP/DOWN CHARACTERISTICS (Over the Operating Range; VCC = 5.0V 10%) PARAMETER CE or WE at VIH , Before Power-Down VCC Fall Time: VPF(MAX) to VPF(MIN) VCC Fall Time: VPF(MIN) to VSO VCC Rise Time: VPF(MIN) to VPF(MAX) Power-up Recover Time Expected Data Retention Time (Oscillator On) SYMBOL tPD tF tFB tR tREC tDR 10 MIN 0 300 10 0 35 TYP MAX UNITS s s s s ms years 5, 6 NOTES 9 of 12 DS1742 POWER-UP/DOWN WAVEFORM TIMING 5-VOLT DEVICE POWER-UP/DOWN CHARACTERISTIC (Over the Operating Range; VCC = 3.3V 10%) PARAMETER CE or WE at VIH , Before Power-Down VCC Fall Time: VPF(MAX) to VPF(MIN) VCC Rise Time: VPF(MIN) to VPF(MAX) Power-up Recovery Time Expected Data Retention Time (Oscillator On) SYMBOL tPD tF tR tREC tDR 10 MIN 0 300 0 35 TYP MAX UNITS s s s ms years 5, 6 NOTES POWER-UP/DOWN WAVEFORM TIMING 3.3-VOLT DEVICE CAPACITANCE PARAMETER Capacitance on all input pins Capacitance on all output pins SYMBOL CIN CO MIN TYP MAX 7 10 (TA = 25C) UNITS pF pF NOTES 10 of 12 DS1742 AC TEST CONDITIONS Output Load: 100 pF + 1TTL Gate Input Pulse Levels: 0.0 to 3.0 Volts Timing Measurement Reference Levels: Input: 1.5V Output: 1.5V Input Pulse Rise and Fall Times: 5 ns NOTES: 1. Voltage referenced to ground. 2. Typical values are at 25C and nominal supplies. 3. Outputs are open. 4. Battery switch-over occurs at the lower of either the battery voltage or VPF. 5. Data retention time is at 25C. 6. Each DS1742 has a built-in switch that disconnects the lithium source until VCC is first applied by the user. The expected tDR is defined as a cumulative time in the absence of VCC starting from the time power is first applied by the user. 7. Real Time Clock Modules can be successfully processed through conventional wave-soldering techniques as long as temperature exposure to the lithium energy source contained within does not exceed +85C. Post-solder cleaning with water washing techniques is acceptable, provided that ultrasonic vibration is not used to prevent damage to the crystal. 11 of 12 DS1742 DS1742 24-PIN PACKAGE 12 of 12 |
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