Datasheet

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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

. If a primary power failure is detected, the device

automatically switches to a backup supply. A lithium

coin-cell battery can be connected to the V

BAT

input

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

Features

♦ 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

DS12885/DS12887/DS12887A/DS12C887/DS12C887A

Real-Time Clocks

______________________________________________

Maxim Integrated Products

DS12885

DS83C520

R/W

GND

X2X1

CRYSTAL

BAT

AD(0–7) SQW

RESET

IRQ

RCLR

MOT

Typical Operating Circuit

19-5213; Rev 4; 4/10

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.

Pin Configurations and Ordering Information appear at end of data sheet.

Summary of content (22 pages)

PAGE 1
9-5213; Rev 4; 4/10 Real-Time Clocks 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 batterybacked 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.
PAGE 2
DS12885/DS12887/DS12887A/DS12C887/DS12C887A Real-Time Clocks ABSOLUTE MAXIMUM RATINGS Voltage Range on VCC Pin Relative to Ground .....-0.3V to +6.0V Operating Temperature Range ................................................... Commercial (noncondensing) .............................0°C to +70°C Operating Temperature Range ................................................... Industrial (noncondensing)...............................-40°C to +85°C Storage Temperature Range EDIP .............................
PAGE 3
Real-Time Clocks (VCC = 0V, VBAT = 3.0V, TA = over the operating range, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS VBAT Current (OSC On); TA = +25°C, VBACKUP = 3.0V IBAT (Note 8) 500 nA VBAT Current (Oscillator Off) IBATDR (Note 8) 100 nA MAX UNITS DC ns AC ELECTRICAL CHARACTERISTICS (VCC = 4.5V to 5.5V, TA = over the operating range.
PAGE 4
Real-Time Clocks DS12885/DS12887/DS12887A/DS12C887/DS12C887A Motorola Bus Read/Write Timing PWASH tASED AS tASD tCYC PWEH PWEL DS tRWS tRWH R/ W tCH tCS CS tDSW tDHW AD0–AD7 WRITE tAHL tASL tDHR AD0–AD7 READ tDDR Intel Bus Write Timing tCYC AS PWASH tASD DS tASD tASED R/W PWEH PWEL tCH tCS CS tASL tAHL tDSW AD0–AD7 WRITE 4 _____________________________________________________________________ tDHW
PAGE 5
Real-Time Clocks tCYC PWASH AS tASD tASED DS PWEH PWEL tASD R/W tCH tCS CS tASL tDHR tDDR tAHL AD0–AD7 IRQ Release Delay Timing DS RESET tRWL IRQ tIRR tIRDS Power-Up/Power-Down Timing VCC VPF(MAX) VPF(MIN) tF tR tRPU tDR INPUTS RECOGNIZED DON'T CARE RECOGNIZED HIGH-Z OUTPUTS VALID VALID _____________________________________________________________________ 5 DS12885/DS12887/DS12887A/DS12C887/DS12C887A Intel Bus Read Timing
PAGE 6
DS12885/DS12887/DS12887A/DS12C887/DS12C887A Real-Time Clocks POWER-UP/POWER-DOWN CHARACTERISTICS (TA = -40°C to +85°C) (Note 2) PARAMETER SYMBOL Recovery at Power-Up CONDITIONS MIN TYP MAX UNITS 200 ms tRPU 20 VCC Fall Time; VPF(MAX) to VPF(MIN) tF 300 µs VCC Rise Time; VPF(MIN) to VPF(MAX) tR 0 µs DATA RETENTION (TA = +25°C) PARAMETER SYMBOL Expected Data Retention CONDITIONS MIN tDR TYP MAX 10 UNITS years CAPACITANCE (TA = +25°C) (Note 9) PARAMETER SYMBOL CONDITIONS MIN
PAGE 7
Real-Time Clocks IBAT1 vs. VBAT vs. TEMPERATURE +85°C 300 32768.70 32768.60 FREQUENCY (Hz) IBAT (nA) +25°C 250 0°C +70°C +40°C 200 3.0 32768.40 32768.30 32768.10 150 2.8 32768.50 32768.20 -40°C 2.5 DS12885 toc02 DS12885 toc01 VCC = 0V OSCILLATOR FREQUENCY vs. VCC 3.5 3.3 VBAT (V) 3.8 32768.00 4.0 4.5 4.8 5.0 5.3 5.
PAGE 8
Real-Time Clocks DS12885/DS12887/DS12887A/DS12C887/DS12C887A Pin Description PIN SO, PDIP PLCC TQFP NAME FUNCTION Motorola or Intel Bus Timing Selector. This pin selects one of two bus types. When connected to VCC, Motorola bus timing is selected. When connected to GND or left disconnected, Intel bus timing is selected. The pin has an internal pulldown resistor. 1 1 2 29 MOT 2 — 3 30 X1 3 — 4 31 X2 Connections for Standard 32.768kHz Quartz Crystal.
PAGE 9
Real-Time Clocks PIN SO, PDIP EDIP PLCC TQFP 22 2, 3, 16, 20, 21, 22 1, 11, 13, 18, 26 4, 6, 10, 15, 20, 23, 25, 27, 32 17 18 17 18 21 22 18 19 NAME N.C. FUNCTION No Connection. This pin should remain unconnected. Pin 21 is RCLR for the DS12887A/DS12C887A. On the EDIP, these pins are missing by design. DS Data Strobe or Read Input. The DS pin has two modes of operation depending on the level of the MOT pin. When the MOT pin is connected to VCC, Motorola bus timing is selected.
PAGE 10
DS12885/DS12887/DS12887A/DS12C887/DS12C887A Real-Time Clocks Pin Description (continued) PIN SO, PDIP 19 20 21 10 EDIP 19 — 21 (DS12887A/ DS12C887A) PLCC 23 24 25 TQFP 21 22 24 NAME FUNCTION IRQ 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
Real-Time Clocks The DS12885 family of RTCs provide 14 bytes of realtime 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 common interrupt output, and a programmable squarewave output are available. 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 VCC.
PAGE 12
DS12885/DS12887/DS12887A/DS12C887/DS12C887A Real-Time Clocks 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.
PAGE 13
Real-Time Clocks condition when at logic 1. An alarm is generated each hour when the don’t-care bits are set in the hours byte. Similarly, an alarm is generated every minute with don’t-care codes in the hours and minute alarm bytes. The don’t-care codes in all three alarm bytes create an interrupt every second. All 128 bytes can be directly written or read, except for the following: 1) Registers C and D are read-only. 2) Bit 7 of register A is read-only. 3) The MSB of the seconds byte is read-only.
PAGE 14
DS12885/DS12887/DS12887A/DS12C887/DS12C887A Real-Time Clocks Table 2B.
PAGE 15
Real-Time Clocks The real-time clocks have four control registers that are accessible at all times, even during the update cycle. Control Register A MSB LSB BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 UIP DV2 DV1 DV0 RS3 RS2 RS1 RS0 Bit 7: Update-In-Progress (UIP). This bit is a status flag that can be monitored. When the UIP bit is a 1, the update transfer occurs soon. When UIP is a 0, the update transfer does not occur for at least 244µs.
PAGE 16
DS12885/DS12887/DS12887A/DS12C887/DS12C887A Real-Time Clocks Control Register B MSB LSB BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 SET PIE AIE UIE SQWE DM 24/12 DSE 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, any update transfer is inhibited, and the program can initialize the time and calendar bytes without an update occurring in the midst of initializing.
PAGE 17
Real-Time Clocks MSB LSB BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 IRQF PF AF UF 0 0 0 0 Bit 7: Interrupt Request Flag (IRQF). This bit is set to 1 when any of the following are true: PF = PIE = 1 AF = AIE = 1 UF = UIE = 1 Any time the IRQF bit is 1, the IRQ pin is driven low. This bit can be cleared by reading Register C or with a RESET. Bit 6: Periodic Interrupt Flag (PF). This bit is readonly and is set to 1 when an edge is detected on the selected tap of the divider chain.
PAGE 18
DS12885/DS12887/DS12887A/DS12C887/DS12C887A Real-Time Clocks Century Register (DS12C887/DS12C887A Only) The century register at location 32h is a BCD register designed to automatically load the BCD value 20 as the year register changes from 99 to 00. The MSB of this register is not affected when the load of 20 occurs, and remains at the value written by the user. Nonvolatile RAM (NV RAM) The general-purpose NV RAM bytes are not dedicated to any special function within the device.
PAGE 19
Real-Time Clocks SELECT BITS REGISTER A tPI PERIODIC INTERRUPT RATE SQW OUTPUT FREQUENCY RS3 RS2 RS1 RS0 0 0 0 0 None None 0 0 0 1 3.90625ms 256Hz 0 0 1 0 7.8125ms 128Hz 0 0 1 1 122.070µs 8.192kHz 0 1 0 0 244.141µs 4.096kHz 0 1 0 1 488.281µs 2.048kHz 0 1 1 0 976.5625µs 1.024kHz 0 1 1 1 1.953125ms 512Hz 1 0 0 0 3.90625ms 256Hz 1 0 0 1 7.8125ms 128Hz 1 0 1 0 15.625ms 64Hz 1 0 1 1 31.25ms 32Hz 1 1 0 0 62.
PAGE 20
Real-Time Clocks DS12885/DS12887/DS12887A/DS12C887/DS12C887A Pin Configurations TOP VIEW MOT 1 24 VCC MOT 1 24 VCC X1 2 23 SQW N.C. 2 23 SQW X2 3 22 N.C. N.C. 3 22 N.C. AD0 4 21 RCLR AD0 4 20 VBAT AD1 5 21 N.C. (RCLR) 20 N.C. 19 IRQ AD2 6 AD3 7 18 RESET AD3 7 AD4 8 17 DS AD4 8 AD5 9 16 GND AD5 9 16 N.C.
PAGE 21
Real-Time Clocks PART TEMP RANGE PIN-PACKAGE DS12885+ 0°C to +70°C 24 PDIP DS12885N+ -40°C to +85°C 24 PDIP DS12885 DS12885Q+ 0°C to +70°C 28 PLCC DS12885Q DS12885QN+ DS12885Q+T&R DS12885QN+T&R DS12885S+ TOP MARK* DS12885 -40°C to +85°C 28 PLCC DS12885Q 0°C to +70°C 28 PLCC DS12885Q -40°C to +85°C 28 PLCC DS12885Q 0°C to +70°C 24 SO (300 mils) DS12885S -40°C to +85°C 24 SO (300 mils) DS12885S DS12885S+T&R 0°C to +70°C 24 SO (300 mils) DS12885S DS12885T+ 0°C to +70°C 32 T
PAGE 22
DS12885/DS12887/DS12887A/DS12C887/DS12C887A Real-Time Clocks Revision History PAGES CHANGED REVISION NUMBER REVISION DATE 0 6/05 Initial release of combined data sheet 1 4/06 Corrected the Intel Bus Write Timing, Intel Bus Read Timing, IRQ Release Delay Timing, Power-Up/Down Timing, and Functional Diagram diagrams; added the Handling, PC Board Layout, and Assembly section. 2 5/06 Corrected the Intel Bus Write Timing diagram; added PLCC pin description information; changed pin 16 from N.C.