Dallas Semiconductor DS1284QN, DS1284Q, DS1284N, DS1284 Datasheet

DS1284

Watchdog Timekeeper Chip

www.dalsemi.com

28-Pin DIP (600-mil)

28-Pin PLCC

13

27

X2A5A3A2A1A0DQ0

DQ1

GND

DQ2VINTB(INTB)

SQW

OE

GND

CE

DQ7

DQ6

DQ5

DQ3

DQ4

1

2

3

4

5

6

7

8

9

10

1112142826

25

24

23

22

21

20

19

18171516X1

NCA4INTAA5A4A3A2

A1

A0

VBAT

RCLR

SQW

OE

GNDCEDQ0

DQ7

NCX2X1

INTA

VCCWEINTB(INTB)

GND

DQ4

25

2423222120

1956

7891011

4 3 2 1 28 27 26

12 13 14 15 16 17 18

RCLR

FEATURES

§ Keeps track of hundredths of seconds,

seconds, minutes, hours, days, date of the
month, months, and years; valid leap year
compensation up to 2100

§ Watchdog timer restarts an out-of-control

processor

§ Alarm function schedules real-time related

activities

§ Programmable interrupts and square wave

outputs maintain 28-pin JEDEC footprint

§ All registers are individually addressable via

the address and data bus

§ Accuracy is better than ±2 minute/month at

25°C

§ 50 bytes of user NV RAM

§ Optional 28-pin PLCC surface mount package

§ Low-power CMOS circuitry is maintained on

less than 0.5 µA when power is supplied from
battery input

§ Optional industrial temperature range

available on 28-pin PLCC (-40°C to +85°C)

PIN ASSIGNMENT

V

BAT

DQ1

DQ2

DQ3

DQ5

DQ6

DS1284

DS1284

PIN DESCRIPTION

- Interrupt Output A (open drain)

INTA

(INTB) - Interrupt Output B (open drain)

INTB

A0-A5 - Address Inputs
DQ0-DQ7 - Data Input/Output

- Chip Enable

CE

- Output Enable

OE

- Write Enable

WE

VCC - +5 Volts
GND - Ground
NC - No Connection
SQW - Square Wave Output
X1,X2 - 32.768 kHz Crystal Connections
V

- +3 Volt Battery Input

BAT

- RAM Clear

RCLR

DESCRIPTION

The DS1284 Watchdog Timekeeper Chip is a self-contained real-time clock, alarm, watchdog timer, and
interval timer in a 28-pin JEDEC DIP package or a 28-pin PLCC surface mount package. An external
crystal and battery are the only components required to maintain time-of-day and memory status in the
absence of power. For a complete description of operating conditions, electrical characteristics, bus

timing, and pin descriptions other than X1, X2, V
data sheet.

BAT

, and

, see the DS1286 Watchdog Timekeeper

RCLR

1 of 3 072799

DS1284

PIN DESCRIPTION

X1, X2 - Connections for a standard 32.768 kHz quartz crystal. The internal oscillator circuitry is
designed for operation with a crystal having a specified load capacitance (CL) of 6 pF. The crystal is
connected directly to the X1 and X2 pins. There is no need for external capacitors or resistors. For more
information on crystal selection and crystal layout considerations, please consult Application Note 58,
“Crystal Considerations with Dallas Real Time Clocks.”

V

- Battery input for any standard 3-volt lithium cell or other energy source. Battery voltage must be

BAT

held between 2.4 and 3.7 volts for proper operation. The nominal write-protect trip point voltage at which
access to registers containing time, watchdog, alarm, and RAM information is denied is set by internal
circuitry as 1.26 x V
size the external energy source. The battery should be connected directly to the V
not be placed in series with the battery to the V
reverse charging current protection circuitry is provided internal to the device and has passed the
requirements of Underwriters Laboratories for UL listing. An optional ground pin is provided for
connection to battery negative. This pin should be grounded but can be left floating.

. A maximum load of 0.5 µA at 25°C in the absence of power should be used to

BAT

pin. A diode must

BAT

pin. Furthermore, a diode is not necessary because

BAT

- The

RCLR

the registers involved with time, alarm, and watchdog functions. In order to clear the RAM,

pin is used to clear (set to logic 1) all 50 bytes of user NV RAM but does not affect

RCLR

RCLR

must

be forced to an input logic 0 (-0. 3 to +0.8 volts) during battery back-up mode when VCC is not applied.
The

function is designed to be used via human interface (shorting to ground or by switch) and not

RCLR

be driven with external buffers. This pin is internally pulled up and should be left floating when not in
use.

DS1284Q 28-PIN PLCC WATCHDOG TIMEKEEPER

PKG 28-PIN

DIM MIN MAX

A IN.MM 0.300 BSC

B IN.MM0.442

D IN.MM0.480

D2 IN.MM0.390

E IN.MM0.090

E2 IN.MM0.390

F IN.MM0.015

H IN.MM0.100

7.62

17.68

12.2

9.91

2.29

9.91

0.38

2.54

0.462

11.73

0.500

12.7

0.430

10.92

0.120

3.05

0.430

10.92

0.020

0.518

0.020

0.518

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