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FM31274-GTR
(Rev.:2011)

5V Integrated Processor Companion with Memory

Ramtron International Corporation 

FM31278/276/274/272 - 5V I2C Companion

Register Map

The RTC and processor companion functions are accessed via 25 special function registers mapped to a separate 2-

wire device ID. The interface protocol is described below. The registers contain timekeeping data, control bits, or

information flags. A description of each register follows the summary table below.

Register Map Summary Table

Nonvolatile =

Battery-backed =

Address

18h

17h

16h

15h

14h

13h

12h

11h

10h

0Fh

0Eh

0Dh

0Ch

0Bh

0Ah

09h

08h

07h

06h

05h

04h

03h

02h

01h

00h

D7

SNL

WDE

WTR

0

0

0

0

0

0

/OSCEN

reserved

D6

D5

D4

D3

Serial Number Byte 7

Serial Number Byte 6

Serial Number Byte 5

Serial Number Byte 4

Serial Number Byte 3

Serial Number Byte 2

Serial Number Byte 1

Serial Number Byte 0

Counter 2 MSB

Counter 2 LSB

Counter 1 MSB

Counter 1 LSB

RC

-

FC

WP1

WP0

-

-

WDT4 WDT3

POR

LB

-

WR3

10 years

0

0

10 mo

0

10 date

0

0

0

0

0

10 hours

10 minutes

10 seconds

reserved CALS CAL4

CAL3

CF reserved reserved reserved

D2

D1

CC

C2P

VBC

-

WDT2 WDT1

WR2

WR1

years

months

date

day

hours

minutes

seconds

CAL2 CAL1

CAL

W

D0

C1P

VTP

WDT0

WR0

CAL0

R

Function

Range

Serial Number 7

FFh

Serial Number 6

FFh

Serial Number 5

FFh

Serial Number 4

FFh

Serial Number 3

FFh

Serial Number 2

FFh

Serial Number 1

FFh

Serial Number 0

FFh

Event Counter 2 MSB FFh

Event Counter 2 LSB FFh

Event Counter 1 MSB FFh

Event Counter 1 LSB FFh

Event Count Control

Companion Control

Watchdog Control

Watchdog Restart/Flags

Years

00-99

Month

1-12

Date

1-31

Day

1-7

Hours

0-23

Minutes

0-59

Seconds

0-59

CAL/Control

RTC Control

Note: When the device is first powered up and programmed, all registers must be written because the battery-

backed register values cannot be guaranteed. The table below shows the default values of the non-volatile

registers. All other register values should be treated as unknown.

Default Register Values

Address Hex Value

18h

0x00

17h

0x00

16h

0x00

15h

0x00

14h

0x00

13h

0x00

12h

0x00

11h

0x00

0Bh

0x00

0Ah

0x1F

01h

0x80

Rev. 2.1

Sept. 2011

Page 11 of 26

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