FM31278/276/274/272 - 5V I2C Companion
Rev. 2.0
Jan. 2011
Page 14 of 26
09h
Watchdog Restart & Flags
D7
D6
D5
D4
D3
D2
D1
D0
WTR
POR
LB
-
WR3
WR2
WR1
WR0
WTR
Watchdog Timer Reset Flag: When a watchdog timer fault occurs, the WTR bit will be 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).
POR
Power-on Reset Flag: When the /RST pin is activated by VDD < VTP, the POR bit will be 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. Battery-backed, 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
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
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
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
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.