AN1012

TIMEKEEPER products

Doc ID 6395 Rev 4

13/33

5.1

Table 2 shows a typical register map for the seconds, minutes, hours, date, day, month, and

year fields. This information is stored in Binary Coded Decimal (BCD) format. These basic

functions are available on all TIMEKEEPER devices. Additional features (e.g., watchdog

timer, alarms, battery low flag, and a wake-up function) have additional registers allocated to

them (such as those shown for the M48T37V/Y in Table 2). The TIMEKEEPER register

locations are constructed from BiPORT™ memory cells which allow data access from two

sides. The on-chip system clock connects to one side (the system side) and the user data is

output to connections on the other (the user’s side). At one-second intervals, clock pulses

are generated by the oscillator and clock chain structure. The system side updates the new

time in the TIMEKEEPER registers. Each TIMEKEEPER register location (e.g. minutes,

hours, day) is then updated as necessary. When the user wants to write a new time, the “W”

bit (the Write bit) of the control register is reset, causing the BiPORT cells to upload the new

system time. The user accesses the TIMEKEEPER and array data by executing standard

READ/WRITE cycles.

The oscillator and clock chain structure consists of a mixture of analog and digital circuitry,

currents drawn as a function of technology and working temperature.

Table 2.

Typical TIMEKEEPER (M48T37V/Y) register map

Table 3.

Address

Data

Function

Range

(in BCD

format)

D7

D6

D5

D4

D3

D2

D1

D0

7FFFh

10 Years

Year

Year

00-99

7FFEh

0

0

0

10M

Month

Month

01-12

7FFDh

0

0

10 Date

Date

Date

01-31

7FFCh

0

FT

0

0

0

Day

Day

01-7

7FFBh

0

0

10 Hours

Hours

Hours

00-23

7FFAh

0

10 Minutes

10 Minutes

Minute

00-59

7FF9h

ST

10 Seconds

Seconds

Second

00-59

7FF8h

W

R

S

Calibration

Control

7FF7h

WDS

BMB4 BMB3 BMB2 BMB1 BMB0

RB1

RB0

Watch

7FF6h

AFE

0

ABE

0

0

0

0

0

Interrupt

7FF5h

RPT4

0

AI 10 Date

Alarm Date

A Date

01-31

7FF4h

RPT3

0

AI 10 Hour

Alarm Hour

A Hour

00-23

7FF3h

RPT2

Alarm 10 Minutes

Alarm Minutes

A Minute

00-59

7FF2h

RPT1

Alarm 10 Seconds

Alarm Seconds

A Second

00-59

7FF1h

1000 Years

100 Years

Century

00-99

7FF0h

WDF

AF

0

BL

Z

Z

Z

Z

Flags

Typical at 20°C

Typical at 70°C

Capacity

Technology

Array

Clock

Array

Clock

64 Kbit

4T Cell

40 nA

497 nA

511 nA

619 nA