FM3135 Integrated RTC/Alarm/FRAM & Embedded Crystal
Cal Output/SquareWave Output
VBAK
When the RTC calibration mode is invoked by
setting the CAL bit (register 00h, bit 2), the ACS
output pin will be driven with a 512 Hz square wave
and the alarm will continue to operate. Since most
users only invoke the calibration mode during
production, this should have no impact on the
otherwise normal operation of the alarm.
1M
Ω
ACS
MCU
FM3135
The ACS output may also be used to drive the system
with a continuous frequency. The AL/SW bit
(register 0Eh, bit 7) must be a ‘0’. A user-selectable
frequency is provided by F0 and F1 (register 0Eh,
bits 5 and 6). The frequencies are 1, 512, 4096, and
32768 Hz. If a continuous frequency output is
enabled by using the 512Hz or SquareWave out
functions, the alarm function will not be available.
Figure 4. ACS Pin Requires Pullup
The ACS pin is an open-drain output that needs to be
pulled up to a supply. The ACS pin and pullup
resistor draws current only when the alarm is
triggered.
Table 4. Alarm Match Bit Examples
Seconds Minutes Hours Date Months Alarm condition
1
0
0
0
0
1
1
0
0
0
1
1
1
0
0
1
1
1
1
0
1
1
1
1
1
No match required = alarm 1/second
Alarm when seconds match = alarm 1/minute
Alarm when seconds, minutes match = alarm 1/hour
Alarm when seconds, minutes, hours match = alarm 1/date
Alarm when seconds, minutes, hours, date match = alarm 1/month
Rev. 1.2
Feb. 2009
Page 7 of 21
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
