FM4005

Rev. 2.3

Oct. 2006

Page 13 of 23

set to 1. It must be cleared by the user. Note that both WTR and POR could be set if both reset sources have

occurred since the flags were cleared by the user. Battery-backed. Read/Write (internally set, user can clear bit).

LB

Low Backup Flag: On power up, if the VBAK source is below the minimum voltage to operate the RTC and event

counters, this bit will be set to 1. The user should clear it to 0 when initializing the system. Battery-backed.

Read/Write (internally set, user can clear bit).

WR3-0

Watchdog Restart: Writing a pattern 1010b to WR3-0 restarts the watchdog timer. The upper nibble contents do

not affect this operation. Writing any pattern other than 1010b to WR3-0 has no effect on the timer. This allows

users to clear the WTR, POR, and LB flags without affecting the watchdog timer. Write-only.

08h

Timekeeping – Years

D7

D6

D5

D4

D3

D2

D1

D0

10 year.3

10 year.2

10 year.1

10 year.0

Year.3

Year.2

Year.1

Year.0

Contains the lower two BCD digits of the year. Lower nibble contains the value for years; upper nibble contains

the value for 10s of years. Each nibble operates from 0 to 9. The range for the register is 0-99. Battery-backed,

read/write.

07h

Timekeeping – Months

D7

D6

D5

D4

D3

D2

D1

D0

0

0

0

10 Month

Month.3

Month.2

Month.1

Month.0

Contains the BCD digits for the month. Lower nibble contains the lower digit and operates from 0 to 9; upper

nibble (one bit) contains the upper digit and operates from 0 to 1. The range for the register is 1-12. Battery-

backed, read/write.

06h

Timekeeping – Date of the month

D7

D6

D5

D4

D3

D2

D1

D0

0

0

10 date.1

10 date.0

Date.3

Date.2

Date.1

Date.0

Contains the BCD digits for the date of the month. Lower nibble contains the lower digit and operates from 0 to 9;

upper nibble contains the upper digit and operates from 0 to 3. The range for the register is 1-31. Battery-backed,

read/write.

05h

Timekeeping – Day of the week

D7

D6

D5

D4

D3

D2

D1

D0

0

0

0

0

0

Day.2

Day.1

Day.0

Lower nibble contains a value that correlates to day of the week. Day of the week is a ring counter that counts

from 1 to 7 then returns to 1. The user must assign meaning to the day value, as the day is not integrated with the

date. Battery-backed, read/write.

04h

Timekeeping – Hours

D7

D6

D5

D4

D3

D2

D1

D0

0

0

10 hours.1

10 hours.0

Hours.3

Hours2

Hours.1

Hours.0

Contains the BCD value of hours in 24-hour format. Lower nibble contains the lower digit and operates from 0 to

9; upper nibble (two bits) contains the upper digit and operates from 0 to 2. The range for the register is 0-23.

Battery-backed, read/write.

03h

Timekeeping – Minutes

D7

D6

D5

D4

D3

D2

D1

D0

0

10 min.2

10 min.1

10 min.0

Min.3

Min.2

Min.1

Min.0

Contains the BCD value of minutes. Lower nibble contains the lower digit and operates from 0 to 9; upper nibble

contains the upper minutes digit and operates from 0 to 5. The range for the register is 0-59. Battery-backed,

read/write.

02h

Timekeeping – Seconds

D7

D6

D5

D4

D3

D2

D1

D0

0

10 sec.2

10 sec.1

10 sec.0

Seconds.3

Seconds.2

Seconds.1

Seconds.0

Contains the BCD value of seconds. Lower nibble contains the lower digit and operates from 0 to 9; upper nibble

contains the upper digit and operates from 0 to 5. The range for the register is 0-59. Battery-backed, read/write.

01h

CAL/Control

D7

D6

D5

D4

D3

D2

D1

D0

OSCEN

Reserved

CALS

CAL.4

CAL.3

CAL.2

CAL.1

CAL.0

/OSCEN

/Oscillator Enable. When set to 1, the oscillator is halted. When set to 0, the oscillator runs. Disabling the

oscillator can save battery power during storage. On a power-up without battery, this bit is set to 1. Battery-

backed, read/write.