FM33256B
Document Number: 001-86213 Rev. *C
Page 21 of 39
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
-
-
CALS
CAL.4
CAL.3
CAL.2
CAL.1
CAL.0
CALS
Calibration Sign: Determines if the calibration adjustment is applied as an addition to or as a subtraction from the
time-base. This bit can be written only when CAL = ‘1’. Nonvolatile, read/write.
CAL(4:0)
Calibration Code: These five bits control the calibration of the clock. These bits can be written only when CAL = ‘1’.
Nonvolatile, read/write.
00h
RTC/Alarm Control
D7
D6
D5
D4
D3
D2
D1
D0
OSCEN
AF
CF
AEN
Reserved
CAL
W
R
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 a V
BAK
source or on a power-up after a
V
BAK
source has been applied, this bit is internally set to '1', which turns off the oscillator. Battery-backed,
read/write.
AF
Alarm Flag: This bit is set to ‘1’ when the time and date match the values stored in the alarm registers with the
Match bit(s) = ‘0’. The user must clear it to '0'. Battery-backed. (internally set, user must clear bit)
CF
Century Overflow Flag: This bit is set to a ‘1’ when the values in the years register overflows from 99 to 00. This
indicates a new century, such as going from 1999 to 2000 or 2099 to 2100. The user should record the new
century information as needed. The user must clear the CF bit to '0'. Battery-backed. (internally set, user must
clear bit)
AEN
Alarm Enable: This bit enables the alarm function. When AEN is set (and CAL cleared), the ACS pin operates as
an active-low alarm. The state of the ACS pin is detailed in
Table 2
. When AEN is cleared, no new alarm events
that set the AF bit will be generated. Clearing the AEN bit does not automatically clear AF. Battery-backed.
CAL
Calibration Setting: When CAL is set to ‘1’, the clock enters calibration mode. When CAL is set to ‘0’, the clock
operates normally, and the ACS pin is controlled by the RTC alarm. Battery-backed, read/write.
W
Write Time. Setting the W bit to ‘1’ freezes updates of the user timekeeping registers. The user can then write them
with updated values. Setting the W bit to ‘0’ causes the contents of the time registers to be transferred to the
timekeeping counters. Battery-backed, read/write.
Table 7. Register Description
(continued)
Address
Description
