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DS12885/DS12887/DS12887A/DS12C887/DS12C887A

Real-Time Clock

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13

The three alarm bytes can be used in two ways. First,
when the alarm time is written in the appropriate hours,
minutes, and seconds alarm locations, the alarm inter-
rupt is initiated at the specified time each day, if the
alarm-enable bit is high. In this mode, the “0” bits in the
alarm registers and the corresponding time registers
must always be written to 0 (Table 2A and 2B). Writing
the 0 bits in the alarm and/or time registers to 1 can
result in undefined operation.

The second use condition is to insert a “don’t care”
state in one or more of the three alarm bytes. The don’t-
care code is any hexadecimal value from C0 to FF. The
two most significant bits of each byte set the don’t-care

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.

Table 2A. Time, Calendar, and Alarm Data Modes—BCD Mode (DM = 0)

ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

FUNCTION

RANGE

00H

0

10 Seconds

Seconds

Seconds

00–59

01H

0

10 Seconds

Seconds

Seconds Alarm

00–59

02H

0

10 Minutes

Minutes

Minutes

00–59

03H

0

10 Minutes

Minutes

Minutes Alarm

00–59

AM/PM

0

10 Hours

04H

0

0

10 Hours

Hours

Hours

1–12 +AM/PM

00–23

AM/PM

0

10 Hours

05H

0

0

10 Hours

Hours

Hours Alarm

1–12 +AM/PM

00–23

06H

0

0

0

0

0

Day

Day

01–07

07H

0

0

10 Date

Date

Date

01–31

08H

0

0

0

10 Months

Month

Month

01–12

09H

10 Years

Year

Year

00–99

0AH

UIP

DV2

DV1

DV0

RS3

RS2

RS1

RS0

Control

0BH

SET

PIE

AIE

UIE

SQWE

DM

24/12

DSE

Control

0CH

IRQF

PF

AF

UF

0

0

0

0

Control

0DH

VRT

0

0

0

0

0

0

0

Control

0EH-31H

X

X

X

X

X

X

X

X

RAM

32H

10 Century

Century

Century*

00–99

33H-7FH

X

X

X

X

X

X

X

X

RAM

X = 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.

Summary of Contents for Maxim DS12885

Page 1: ...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 i...

Page 2: ...densing 0 C to 70 C Operating Temperature Range Industrial noncondensing 40 C to 85 C Storage Temperature Range 55 C to 125 C Soldering Temperature See IPC JEDEC J STD 020 Specification Note 1 Solderi...

Page 3: ...ITS Cycle Time tCYC 385 DC ns Pulse Width DS Low or R W High PWEL 150 ns Pulse Width DS High or R W Low PWEH 125 ns Input Rise and Fall tR tF 30 ns R W Hold Time tRWH 10 ns R W Setup Time Before DS E...

Page 4: ...________________________________ PWASH PWEL tASED tCYC tRWS tCS tRWH tCH PWEH tASD AD0 AD7 READ CS R W AS DS AD0 AD7 WRITE tDHW tDHR tDDR tAHL tASL tDSW Motorola Bus Read Write Timing Intel Bus Write...

Page 5: ...__________________ 5 tCS tAHL tASL tCYC PWASH PWEL PWEH CS R W AS DS AD0 AD7 tASD tASD tASED tDDR tDHR tCH Intel Bus Read Timing tRWL tIRR tIRDS DS RESET IRQ IRQ Release Delay Timing OUTPUTS INPUTS HI...

Page 6: ...mum and VIH minimum Input Pulse Rise and Fall Times 5ns WARNING Negative undershoots below 0 3V while the part is in battery backed mode may cause loss of data Note 1 RTC modules can be successfully p...

Page 7: ...32768 60 32768 70 32768 00 4 5 5 5 IBAT1 vs VBAT vs TEMPERATURE DS12885 toc01 VBAT V I BAT nA 3 8 2 8 3 0 3 3 3 5 200 300 250 150 2 5 4 0 VCC 0V 85 C 25 C 0 C 40 C 70 C 40 C POWER CONTROL GND OSC BUS...

Page 8: ...S transitions high in the case of Intel timing 12 16 12 15 20 12 17 GND Ground 13 13 16 13 CS Active Low Chip Select Input The chip select signal must be asserted low for a bus cycle in the device to...

Page 9: ...tive Low Reset Input The RESET pin has no effect on the clock calendar or RAM On power up the RESET pin can be held low for a time to allow the power supply to stabilize The amount of time that RESET...

Page 10: ...attery directly to the VBAT pin Diodes in series between the VBAT pin and the battery may prevent proper operation UL recognized to ensure against reverse charging when used with a lithium battery 21...

Page 11: ...uit does not require any external resistors or capacitors to operate Table 1 specifies several crys tal parameters for the external crystal Figure 1 shows a functional schematic of the oscillator circ...

Page 12: ...bytes can be either binary or binary coded decimal BCD format The day of week register increments at midnight incre menting from 1 through 7 The day of week register is used by the daylight saving fu...

Page 13: ...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 Table 2A Time Calendar and Alarm Data Modes BCD Mode DM...

Page 14: ...0 0 Day Day 01 07 07H 0 0 0 Date Date 01 1F 08H 0 0 0 0 Month Month 01 0C 09H 0 Year Year 00 63 0AH UIP DV2 DV1 DV0 RS3 RS2 RS1 RS0 Control 0BH SET PIE AIE UIE SQWE DM 24 12 DSE Control 0CH IRQF PF A...

Page 15: ...ime A pattern of 11x enables the oscillator but holds the countdown chain in reset The next update occurs at 500ms after a pattern of 010 is written to DV0 DV1 and DV2 Bits 3 to 0 Rate Selector RS3 RS...

Page 16: ...te end flag UF bit in Register C to assert IRQ The RESET pin going low or the SET bit going high clears the UIE bit The internal functions of the device do not affect the UIE bit but is cleared to 0 o...

Page 17: ...in goes low and a 1 appears in the IRQF bit This bit can be cleared by reading Register C or with a RESET Bit 5 Update Ended Interrupt Flag UF This bit is set after each update cycle When the UIE bit...

Page 18: ...at are set high are cleared when read and new interrupts that are pending during the read cycle are held until after the cycle is completed One two or three bits can be set when reading Register C Eac...

Page 19: ...s read on the UIP bit the user has at least 244 s before the time calendar data is changed Therefore the user should avoid interrupt service rou tines that would cause the time needed to read valid ti...

Page 20: ...C N C MOT N C IRQ RESET DS AD4 AD3 AD2 AD1 N C R W AS CS FOR THE DS12887A DS12C887A NOTE THE DS12887A AND DS12C887A CANNOT BE STORED OR SHIPPED IN CONDUCTIVE MATERIAL THAT WILL GIVE A CONTINUITY PATH...

Page 21: ...DS12885QN 40 C to 85 C 28 PLCC DS12885Q DS12885QN 40 C to 85 C 28 PLCC DS12885Q DS12885Q T R 0 C to 70 C 28 PLCC DS12885Q DS12885Q T R 0 C to 70 C 28 PLCC DS12885Q DS12885QN T R 40 C to 85 C 28 PLCC...

Page 22: ...trademark of Dallas Semiconductor Corporation Quijano Revision History Rev 0 6 05 Initial release of combined data sheet Rev 1 4 06 Corrected Intel Bus Write Timing diagram page 4 Intel Bus Read Timin...

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