Dallas Maxim DS12885 Manual

Real-time clock

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Rev 3; 2/07
General Description
The DS12885, DS12887, and DS12C887 real-time
clocks (RTCs) are designed to be direct replacements
for the DS1285 and DS1287. The devices provide a
real-time clock/calendar, one time-of-day alarm, three
maskable interrupts with a common interrupt output, a
programmable square wave, and 114 bytes of battery-
backed static RAM (113 bytes in the DS12C887 and
DS12C887A). The DS12887 integrates a quartz crystal
and lithium energy source into a 24-pin encapsulated
DIP package. The DS12C887 adds a century byte at
address 32h. For all devices, the date at the end of the
month is automatically adjusted for months with fewer
than 31 days, including correction for leap years. The
devices also operate in either 24-hour or
12-hour format with an AM/PM indicator. A precision
temperature-compensated circuit monitors the status of
V
. If a primary power failure is detected, the device
CC
automatically switches to a backup supply. A lithium
coin-cell battery can be connected to the V
pin on the DS12885 to maintain time and date operation
when primary power is absent. The device is accessed
through a multiplexed byte-wide interface, which sup-
ports both Intel and Motorola modes.
Embedded Systems
Utility Meters
Security Systems
Network Hubs, Bridges, and Routers
Typical Operating Circuit
X1
AS
R/W
DS
DS83C520
CS
AD(0–7)
IRQ
MOT
Pin Configurations and Ordering Information appear at end of data sheet.
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
input
BAT
Applications
CRYSTAL
V
CC
X2
V
CC
RESET
RCLR
DS12885
SQW
V
BAT
GND
______________________________________________ Maxim Integrated Products
Real-Time Clock
♦ Drop-In Replacement for IBM AT Computer
Clock/Calendar
♦ RTC Counts Seconds, Minutes, Hours, Day, Date,
Month, and Year with Leap Year Compensation
Through 2099
♦ Binary or BCD Time Representation
♦ 12-Hour or 24-Hour Clock with AM and PM in
12-Hour Mode
♦ Daylight Saving Time Option
♦ Selectable Intel or Motorola Bus Timing
♦ Interfaced with Software as 128 RAM Locations
♦ 14 Bytes of Clock and Control Registers
♦ 114 Bytes of General-Purpose, Battery-Backed
RAM (113 Bytes in the DS12C887 and
DS12C887A)
♦ RAM Clear Function (DS12885, DS12887A, and
DS12C887A)
♦ Interrupt Output with Three Independently
Maskable Interrupt Flags
♦ Time-of-Day Alarm Once Per Second to Once
Per Day
♦ Periodic Rates from 122μs to 500ms
♦ End-of-Clock Update Cycle Flag
♦ Programmable Square-Wave Output
♦ Automatic Power-Fail Detect and Switch Circuitry
♦ Optional 28-Pin PLCC Surface Mount Package or
32-Pin TQFP (DS12885)
♦ Optional Encapsulated DIP (EDIP) Package with
Integrated Crystal and Battery (DS12887,
DS12887A, DS12C887, DS12C887A)
♦ Optional Industrial Temperature Range Available
♦ Underwriters Laboratory (UL) Recognized
Features
1

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Summary of Contents for Dallas Maxim DS12885

  • Page 1 ♦ Optional Industrial Temperature Range Available AD(0–7) ♦ Underwriters Laboratory (UL) Recognized Pin Configurations and Ordering Information appear at end of data sheet. ______________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
  • Page 2: Absolute Maximum Ratings

    Real-Time Clock ABSOLUTE MAXIMUM RATINGS Voltage Range on V Pin Relative to Ground ..-0.3V to +6.0V Storage Temperature Range ......-55°C to +125°C Operating Temperature Range ........... Soldering Temperature ........See IPC/JEDEC Commercial (noncondensing) ......0°C to +70°C J-STD-020 Specification (Note 1) Operating Temperature Range ........... Soldering Temperature (leads, 10s) ........+260°C Industrial (noncondensing).......-40°C to +85°C Stresses beyond those listed under “Absolute Maximum Ratings”...
  • Page 3: Ac Electrical Characteristics

    Real-Time Clock DC ELECTRICAL CHARACTERISTICS = 0V, V = 3.0V, T = over the operating range, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS UNITS Current (OSC On); (Note 8) = +25°C, V = 3.0V BACKUP Current (Oscillator Off) (Note 8) BATDR AC ELECTRICAL CHARACTERISTICS = 4.5V to 5.5V, T...
  • Page 4 Real-Time Clock Motorola Bus Read/Write Timing ASED R/ W AD0–AD7 WRITE AD0–AD7 READ Intel Bus Write Timing ASED AD0–AD7 WRITE _____________________________________________________________________...
  • Page 5 Real-Time Clock Intel Bus Read Timing ASED AD0–AD7 IRQ Release Delay Timing RESET IRDS Power-Up/Power-Down Timing PF(MAX) PF(MIN) DON'T CARE RECOGNIZED RECOGNIZED INPUTS HIGH-Z VALID OUTPUTS VALID _____________________________________________________________________...
  • Page 6: Data Retention

    Real-Time Clock POWER-UP/POWER-DOWN CHARACTERISTICS = -40°C to +85°C) (Note 2) PARAMETER SYMBOL CONDITIONS UNITS Recovery at Power-Up Fall Time; V PF(MAX) µs PF(MIN) Rise Time; V PF(MIN) µs PF(MAX) DATA RETENTION = +25°C) PARAMETER SYMBOL CONDITIONS UNITS Expected Data Retention years CAPACITANCE = +25°C) (Note 9)
  • Page 7: Typical Operating Characteristics

    Real-Time Clock Typical Operating Characteristics = +5.0V, T = +25°C, unless otherwise noted.) vs. V BAT1 OSCILLATOR FREQUENCY vs. TEMPERATURE vs. V = 0V +85°C 32768.70 32768.60 +25°C 32768.50 32768.40 0°C +70°C 32768.30 +40°C 32768.20 32768.10 -40°C 32768.00 Functional Diagram DIVIDE DIVIDE DIVIDE...
  • Page 8: Pin Description

    Real-Time Clock Pin Description NAME FUNCTION EDIP PLCC TQFP PDIP Motorola or Intel Bus Timing Selector. This pin selects one of two bus types. When connected to V , Motorola bus timing is selected. When connected to GND or left disconnected, Intel bus timing is selected. The pin has an internal pulldown resistor.
  • Page 9 Real-Time Clock Pin Description (continued) NAME FUNCTION EDIP PLCC TQFP PDIP 4, 6, 10, 2, 3, 1, 11, No Connection. This pin should remain unconnected. Pin 21 is RCLR for the 15, 20, 16, 20, 13, 18, N.C. 23, 25, DS12887A/DS12C887A.
  • Page 10 Real-Time Clock Pin Description (continued) NAME FUNCTION EDIP PLCC TQFP PDIP Active-Low Interrupt Request Output. The IRQ pin is an active-low output of the device that can be used as an interrupt input to a processor. The IRQ output remains low as long as the status bit causing the interrupt is present and the corresponding interrupt-enable bit is set.
  • Page 11: Detailed Description

    RF generating signals. Refer to Application Note 58: up supply. The backup supply input supports a primary Crystal Considerations for Dallas Real-Time Clocks for additional specifications. battery, such as lithium coin cell. The devices are accessed through a multiplexed address/data bus that supports Intel and Motorola modes.
  • Page 12: Clock Accuracy

    Figure 2 shows a typical PC board layout for isolation of the crystal and oscillator from noise. Refer to NOTE: AVOID ROUTING SIGNAL LINES Application Note 58: Crystal Considerations with Dallas IN THE CROSSHATCHED AREA (UPPER LEFT QUADRANT) OF Real-Time Clocks for more detailed information.
  • Page 13 Real-Time Clock The three alarm bytes can be used in two ways. First, condition when at logic 1. An alarm is generated each when the alarm time is written in the appropriate hours, hour when the don’t-care bits are set in the hours byte. minutes, and seconds alarm locations, the alarm inter- Similarly, an alarm is generated every minute with rupt is initiated at the specified time each day, if the...
  • Page 14 Real-Time Clock Table 2B. Time, Calendar, and Alarm Data Modes—Binary Mode (DM = 1) ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 FUNCTION RANGE Seconds Seconds 00–3B Seconds Seconds Alarm 00–3B Minutes Minutes 00–3B...
  • Page 15: Control Registers

    Real-Time Clock Control Registers The real-time clocks have four control registers that are accessible at all times, even during the update cycle. Control Register A BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 Bit 7: Update-In-Progress (UIP).
  • Page 16 Real-Time Clock Control Register B BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 SQWE 24/12 Bit 7: SET. When the SET bit is 0, the update transfer Bit 3: Square-Wave Enable (SQWE). When this bit is functions normally by advancing the counts once per set to 1, a square-wave signal at the frequency set by second.
  • Page 17 Real-Time Clock Control Register C BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 IRQF Bit 7: Interrupt Request Flag (IRQF). This bit is set to Bit 5: Alarm Interrupt Flag (AF). A 1 in the AF bit indi- 1 when any of the following are true: cates that the current time has matched the alarm time.
  • Page 18: Nonvolatile Ram (Nv Ram)

    Real-Time Clock Century Register when reading Register C. Each used flag bit should be examined when Register C is read to ensure that no (DS12C887/DS12C887A Only) interrupts are lost. The century register at location 32h is a BCD register The second flag bit method is used with fully enabled designed to automatically load the BCD value 20 as the interrupts.
  • Page 19 Real-Time Clock sponding time byte and issues an alarm if a match or if Table 3. Periodic Interrupt Rate and a don’t-care code is present in all three positions. Square-Wave Output Frequency There are three methods that can handle RTC access SELECT BITS PERIODIC that avoid any possibility of accessing inconsistent time...
  • Page 20: Pin Configurations

    Real-Time Clock Pin Configurations TOP VIEW N.C. N.C. N.C. N.C. N.C. RCLR (RCLR) N.C. DS12885 DS12887 DS12885S DS12887A RESET RESET DS12C887 DS12C887A N.C. SO, PDIP EDIP ( ) FOR THE DS12887A/DS12C887A. N.C. N.C. N.C. DS12885Q N.C. PLCC NOTE: THE DS12887A AND DS12C887A CANNOT BE STORED OR SHIPPED IN CONDUCTIVE MATERIAL THAT WILL GIVE A CONTINUITY PATH BETWEEN THE RAM CLEAR PIN AND GROUND.
  • Page 21: Ordering Information

    Real-Time Clock Pin Configurations (continued) Ordering Information PIN- PART TEMP RANGE TOP VIEW PACKAGE MARK* DS12885 0°C to +70°C 24 PDIP DS12885 DS12885+ 0°C to +70°C 24 PDIP DS12885 DS12885N -40°C to +85°C 24 PDIP DS12885 DS12885N+ -40°C to +85°C 24 PDIP DS12885 24 RCLR...
  • Page 22: Revision History

    Maxim reserves the right to change the circuitry and specifications without notice at any time. 22 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc. is a registered trademark of Dallas Semiconductor Corporation. Quijano...

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