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012700

FEATURES

Integrated NV SRAM, real time clock, crystal,

power-fail control circuit and lithium energy

source

Clock registers are accessed identically to the

static RAM; these registers are resident in the

16 top RAM locations

Century byte register; i.e., Y2K complaint

Totally nonvolatile with over 10 years of

operation in the absence of power

Precision power-on reset

Programmable watchdog timer and RTC alarm

BCD coded year, month, date, day, hours,

minutes, and seconds with automatic leap year

compensation valid up to the year 2100

Battery voltage level indicator flag

Power-fail write protection allows for

±10%

Lithium energy source is electrically

disconnected to retain freshness until power is

applied for the first time

ORDERING INFORMATION

DS1557P-XXX

(5-Volt)

-70

70 ns access

-100

100 ns access

*DS1557WP-XXX

(3.3 Volt)

-120

120 ns access

-150

150 ns access

*DS9034PCX (PowerCap) Required:

must be ordered seperately

PIN ASSIGNMENT

PIN DESCRIPTION

A0-A14

- Address Input

DQ0-DQ7

- Data Input/Outputs

IRQ

\FT

- Interrupt, Frequency Test

Output (Open Drain)

RST

- Power-On Reset Output

(Open Drain)

CE

- Chip Enable

OE

- Output Enable

WE

- Write Enable

- Power Supply Input

GND

- Ground

NC

- No Connection

X1, X2

- Crystal Connection

- Battery Connection

DESCRIPTION

The DS1557 is a full function, year 2000-compliant (Y2KC), real-time clock/calendar (RTC) with a RTC

alarm, watchdog timer, power-on reset, battery monitor, and 512k x 8 non-volatile static RAM. User

access to all registers within the DS1557 is accomplished with a bytewide interface as shown in Figure 1.

The RTC Registers contain century, year, month, date, day, hours, minutes, and seconds data in 24-hour

BCD format. Corrections for day of month and leap year are made automatically.

DS1557

4MEG NV Y2KC Timekeeping RAM

PRELIMINARY

www.dalsemi.com

1

IRQ/FT

2

3

A15

A16

RST

WE

OE

CE

DQ7

DQ6

DQ5

DQ4

DQ3

DQ2

DQ1

DQ0

GND

4

5

6

7

8

9

10

11

12

13

14

15

16

17

A17

A14

33

32

31

30

29

28

27

26

25

24

23

22

21

20

19

18

A13

A12

A11

A10

A9

A8

A7

A6

A5

A4

A3

A2

A1

A0

34

A18

X1

X2

34-Pin POWERCAP MODULE BOARD

(USES DS9034PCX POWERCAP)