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DS12885/DS12887/DS12887A/DS12C887/DS12C887A

Real-Time Clock

10

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Pin Description (continued)

PIN

SO,

PDIP

EDIP

PLCC

TQFP

NAME

FUNCTION

19

19

23

21

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. The processor program normally
reads the C register to clear the 

IRQ

 pin. The 

RESET

 pin also clears pending

interrupts. When no interrupt conditions are present, the 

IRQ

 level is in the high-

impedance state. Multiple interrupting devices can be connected to an 

IRQ

bus, provided that they are all open drain. The 

IRQ

 pin is an open-drain output

and requires an external pullup resistor to V

CC

.

20

24

22

V

BAT

Connection for a Primary Battery. (DS12885 Only.) Battery voltage must be held
between the minimum and maximum limits for proper operation. If a backup
supply is not supplied, V

BAT

 must be grounded. Connect the battery directly to

the V

BAT

 pin. Diodes in series between the V

BAT

 pin and the battery may

prevent proper operation. UL recognized to ensure against reverse charging
when used with a lithium battery.

21

21

 (DS12887A/

DS12C887A)

25

24

RCLR

Active-Low RAM Clear. The 

RCLR

 pin is used to clear (set to logic 1) all the

general-purpose RAM, but does not affect the RAM associated with the RTC. To
clear the RAM, 

RCLR

 must be forced to an input logic 0 during battery-backup

mode when V

CC

 is not applied. The 

RCLR

 function is designed to be used

through a human interface (shorting to ground manually or by a switch) and not
to be driven with external buffers. This pin is internally pulled up. Do not use an
external pullup resistor on this pin.

23

23

27

26

SQW

Square-Wave Output. The SQW pin can output a signal from one of 13 taps
provided by the 15 internal divider stages of the RTC. The frequency of the
SQW pin can be changed by programming Register A, as shown in Table 1.
The SQW signal can be turned on and off using the SQWE bit in Register B. The
SQW signal is not available when V

CC 

is less than V

PF

.

24

24

28

28

V

CC

DC Power Pin for Primary Power Supply. When V

CC

 is applied within normal

limits, the device is fully accessible and data can be written and read. When
V

CC

 is below V

PF

 reads and writes are inhibited.

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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