DS1556 1M, Nonvolatile, Y2K-Compliant Timekeeping RAM

2 of 20

PIN DESCRIPTION

A0–A16

- 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

N.C.

- No Connection

X1, X2

- Crystal Connection

- Battery Connection

ORDERING INFORMATION

PART

TEMP RANGE

OPERATING

VOLTAGE

(V)

PIN-PACKAGE

TOP MARK

DS1556-70

0°C to +70°C

5

32 EDIP (0.740a)

DS1556-070

DS1556-70IND

-40°C to +85°C

5

32 EDIP (0.740a)

DS1556-070 IND

DS1556P-70

0°C to +70°C

5

34 PowerCap

DS1556P-070

DS1556P-70IND

-40°C to +85°C

5

34 PowerCap

DS1556P-070 IND

DS1556W-120

0°C to +70°C

3.3

32 EDIP (0.740a)

DS1556W-120

DS1556W-120IND

-40°C to +85°C

3.3

32 EDIP (0.740a)

DS1556W-120 IND

DS1556WP-120

0°C to +70°C

3.3

34 PowerCap

DS1556WP-120

DS1556WP-120IND

-40°C to +85°C

3.3

34 PowerCap

DS1556WP-120 IND

DESCRIPTION

The DS1556 is a full-function, year-2000-compliant (Y2KC), real-time clock/calendar (RTC) with an

RTC alarm, watchdog timer, power-on reset, battery monitor, and 128k x 8 nonvolatile static RAM. User

access to all registers within the DS1556 is accomplished with a byte-wide 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.

The RTC registers are double-buffered into an internal and external set. The user has direct access to the

external set. Clock/calendar updates to the external set of registers can be disabled and enabled to allow

the user to access static data. Assuming the internal oscillator is turned on, the internal set of registers is

continuously updated, which occurs regardless of external registers settings to guarantee that accurate

RTC information is always maintained.