FM31278/276/274/272 - 5V I2C Companion
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.
Reserved
CALS
Reserved bits. Do not use. Should remain set to 0.
Calibration sign. Determines if the calibration adjustment is applied as an addition to or as a subtraction from
the time-base. Calibration is explained on page 7. Nonvolatile, read/write.
These five bits control the calibration of the clock. Nonvolatile, read/write.
CAL.4-0
00h
Flags/Control
D7
D6
D5
D4
D3
D2
D1
D0
Reserved
CF
Reserved
Reserved
Reserved
CAL
W
R
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. This bit is cleared to 0 when the Flag register is read. It is read-only for the user.
Battery-backed.
Calibration Mode. When set to 1, the clock enters calibration mode. When CAL is set to 0, the clock operates
normally, and the CAL/PFO pin is controlled by the power fail comparator. Battery-backed, read/write.
Write Time. Setting the W bit to 1 freezes the clock. The user can then write the timekeeping registers with
updated values. Resetting the W bit to 0 causes the contents of the time registers to be transferred to the
timekeeping counters and restarts the clock. Battery-backed, read/write.
CAL
W
R
Read Time. Setting the R bit to 1 copies a static image of the timekeeping core and place it into the user
registers. The user can then read them without concerns over changing values causing system errors. The R bit
going from 0 to 1 causes the timekeeping capture, so the bit must be returned to 0 prior to reading again.
Battery-backed, read/write.
Reserved
Reserved bits. Do not use. Should remain set to 0.
Rev. 2.0
Dec. 2007
Page 14 of 25
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
