DS12887

Manufacturer Part NumberDS12887
DescriptionThe DS12885, DS12887, and DS12C887 real-time clocks (RTCs) are designed to be direct replacements for the DS1285 and DS1287
ManufacturerMaxim
DS12887 datasheet
 


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19-5213; Rev 4; 4/10
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.
Applications
Embedded Systems
Utility Meters
Security Systems
Network Hubs, Bridges, and Routers
Typical Operating Circuit
CRYSTAL
X1
X2
AS
R/W
DS
DS83C520
DS12885
CS
AD(0–7)
IRQ
MOT
GND
Pin Configurations and Ordering Information appear at end of data sheet.
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
♦ 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
input
BAT
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
V
CC
♦ Automatic Power-Fail Detect and Switch Circuitry
♦ Optional 28-Pin PLCC Surface Mount Package or
V
CC
32-Pin TQFP (DS12885)
RESET
♦ Optional Encapsulated DIP (EDIP) Package with
RCLR
Integrated Crystal and Battery (DS12887,
DS12887A, DS12C887, DS12C887A)
♦ Optional Industrial Temperature Range Available
SQW
♦ Underwriters Laboratory (UL) Recognized
V
BAT
______________________________________________ Maxim Integrated Products
Real-Time Clocks
Features
1

DS12887 Summary of contents

  • Page 1

    ... 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 ...

  • Page 2

    ... PDIP, SO, PLCC, TQFP ..................................-55°C to +125°C 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 absolute maximum rating conditions for extended periods may affect device reliability ...

  • Page 3

    DC ELECTRICAL CHARACTERISTICS ( 3.0V over the operating range, unless otherwise noted.) (Note 2) CC BAT A PARAMETER SYMBOL V Current (OSC On); BAT T = +25° 3.0V A BACKUP V Current ...

  • Page 4

    Real-Time Clocks AS t ASD AD0–AD7 WRITE AD0–AD7 READ AS t ASD DS t ASD R ASL AD0–AD7 WRITE 4 _____________________________________________________________________ Motorola Bus Read/Write Timing PW ASH t ASED t CYC ...

  • Page 5

    AS t ASD DS t ASD R/W CS AD0–AD7 IRQ Release Delay Timing DS RESET IRQ t IRDS PF(MAX) V PF(MIN) RECOGNIZED INPUTS VALID OUTPUTS t CYC PW ASH t ASED ...

  • Page 6

    ... DR CONDITIONS 3.0V 50pF + 1TTL Gate Input/Output: V 5ns ; MOT, AS, AD0–AD7 = MIN TYP MAX 20 200 300 0 MIN TYP MAX 10 MIN TYP MAX 5 7 TEST CONDITIONS maximum and V minimum IL IH open. BACKUP UNITS ms µs µs UNITS years UNITS pF pF ...

  • Page 7

    T = +25°C, unless otherwise noted vs. V BAT1 BAT vs. TEMPERATURE +85°C CC 300 250 0°C +70°C +40°C 200 -40°C 150 2.5 2.8 3.0 3.5 3.3 V (V) BAT X1 ...

  • Page 8

    Real-Time Clocks PIN SO, EDIP PLCC TQFP PDIP — — 5–10, 4–11 4– 15, 20 12, 17 ...

  • Page 9

    ... No Connection. This pin should remain unconnected. Pin 21 is RCLR for the N.C. DS12887A/DS12C887A. On the EDIP, these pins are missing by design. D ata Read Inp ut. The has ati end the l evel of the hen the connected sel ected ...

  • Page 10

    ... Real-Time Clocks PIN SO, EDIP PLCC TQFP PDIP — (DS12887A DS12C887A ____________________________________________________________________ Pin Description (continued) NAME 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 The DS12885 family of RTCs provide 14 bytes of real- time clock/calendar, alarm, and control/status registers and 114 bytes (113 bytes for DS12C887 and DS12C887A) of nonvolatile, battery-backed static RAM. A time-of-day alarm, three maskable interrupts with a ...

  • Page 12

    ... Refer to Application Note 58: Crystal Considerations with Dallas Real-Time Clocks for more detailed information. Clock Accuracy for DS12887, DS12887A, DS12C887, DS12C887A Only The encapsulated DIP modules are trimmed at the fac- tory to an accuracy of ±1 minute per month at +25°C. ...

  • Page 13

    ... Read/Write Bit. * DS12C887, DS12C887A only. General-purpose RAM on DS12885, DS12887, and DS12887A. Note: Unless otherwise specified, the state of the registers is not defined when power is first applied. Except for the seconds regis- ter, 0 bits in the time and date registers can be written to 1, but may be modified when the clock updates. 0 bits should always be written to 0 except for alarm mask bits ...

  • Page 14

    ... Read/Write Bit. * DS12C887, DS12C887A only. General-purpose RAM on DS12885, DS12887, and DS12887A. Note: Unless otherwise specified, the state of the registers is not defined when power is first applied. Except for the seconds regis- ter, 0 bits in the time and date registers can be written to 1, but may be modified when the clock updates. 0 bits should always be written to 0 except for alarm mask bits ...

  • Page 15

    Control Registers The real-time clocks have four control registers that are accessible at all times, even during the update cycle. MSB BIT 7 BIT 6 BIT 5 UIP DV2 Bit 7: Update-In-Progress (UIP). This bit is a status flag that ...

  • Page 16

    Real-Time Clocks MSB BIT 7 BIT 6 BIT 5 SET PIE Bit 7: SET. When the SET bit is 0, the update transfer functions normally by advancing the counts once per second. When the SET bit is written to 1, ...

  • Page 17

    MSB BIT 7 BIT 6 BIT 5 IRQF PF Bit 7: Interrupt Request Flag (IRQF). This bit is set to 1 when any of the following are true PIE = AIE = ...

  • Page 18

    ... The act of reading Register C clears all active flag bits and the IRQF bit. Interrupts When the DS12887, DS12887A, DS12C887, and DS12C887A are shipped from the factory, the internal oscillator is turned off. This prevents the lithium energy cell from being used until the device is installed in a system ...

  • Page 19

    Table 3. Periodic Interrupt Rate and Square-Wave Output Frequency SELECT BITS t PERIODIC PI REGISTER A INTERRUPT RATE RS3 RS2 RS1 RS0 None 3.90625ms 7.8125ms ...

  • Page 20

    ... DS12885 AD2 6 DS12885S AD3 7 AD4 8 AD5 9 AD6 10 AD7 11 GND 12 SO, PDIP 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. 20 ____________________________________________________________________ SQW 22 N.C. 21 RCLR 20 V BAT 19 ...

  • Page 21

    ... SUBSTRATE CONNECTED TO GROUND ____________________________________________________________________ Real-Time Clocks Ordering Information TOP MARK* DS12885 DS12885 DS12885Q DS12885Q DS12885Q DS12885Q DS12885S DS12885S DS12885S DS12885 DS12885 DS12887 DS12887A DS12C887 DS12C887AA Thermal Information THETA-JA (°C/W) THETA-JC (°C/ 105 Package Information PACKAGE CODE DOCUMENT NO. W24+1 21-0042 ...

  • Page 22

    ... Ordering Information table. Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. ...