FM3135 Integrated RTC/Alarm/FRAM & Embedded Crystal

Rev. 1.2

Feb. 2009

Page 11 of 21

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. Battery-backed, 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. Battery-backed, read/write.

00h

RTC/Alarm Control

D7

D6

D5

D4

D3

D2

D1

D0

LB

AF

CF

POR

AEN

CAL

W

R

LB

will be set to ‘1’. All registers need to be re-initialized since the battery-backed register values should be

treated as unknown. The user should clear it to ‘0’ when initializing the system. Battery-backed. Read/Write

(internally set, user can clear bit by writing to a ‘0’).

AF

Alarm Flag: This read-only bit is set to 1 when the time/date match the values stored in the alarm registers with

the Match bit(s) = 0. It is cleared when the RTC/Alarm Control register is read. Battery-backed.

CF

Century Overflow Flag: This read-only 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 when the RTC/Alarm Control register is read.

Battery-backed.

POR

Read/Write (internally set, user can clear bit by writing to a ‘0’).

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 and the AF flag function is enabled. The function of the ACS pin is detailed in Table 3.

When AEN is cleared, no new alarm events will occur but the AF flag and ACS pin will not be cleared.

Battery-backed, read/write.

CAL

Calibration Mode: 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 RTC: 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.

R

Read RTC: 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.