FM3130 Integrated RTC/Alarm with 64Kb FRAM
Cal Output/SquareWave Output
second. Setting the match select bit for seconds to „0‟
causes the logic to match the seconds alarm value to
the current time of day. Since a match will occur for
only one value per minute, the alarm occurs once per
minute. Likewise setting the seconds and minutes
match select bits causes an exact match of these
values. Thus, an alarm will occur once per hour.
Setting seconds, minutes, and hours causes a match
once per day. See Table 4 for other alarm setting
examples.
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.
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.
Function of the ACS Pin
The ACS pin is a multifunction pin. The alarm,
calibration, and square wave functions all share this
output. There are two ways a user can detect an alarm
event, by reading the AF flag or by monitoring the
ACS pin. An interrupt pin on the host processor may
be used to detect an alarm event. The AF flag in the
register 00h (bit 6) will indicate that a time/date
match has occurred. When a match occurs, the AF
bit will be set to „1‟ and the ACS pin will drive low.
The flag and ACS pin will remain in this state until
the RTC/Alarm Control register is read which clears
the AF bit.
VBAK
E
1M
T
t
ACS
MCU
n
FM3130
Table 3 that shows the relationship between register
control settings and the function of the ACS pin.
e
E
m
4
L
e
Figure 4. ACS Pin Requires Pullup
Table 3. Control Bit Settings for ACS Pin
6
c
State of Register Bit
Function of
ACS pin
The ACS pin is an open-drain output that needs to be
1
a
l
pulled up to a supply. The ACS pin and pullup
CAL AEN AL/SW
3
resistor drawspcurrent only when the alarm is
O
0
0
1
0
1
X
X
0
1
0
X
1
/Alarm
Sq Wave out
512 Hz out
triggered.
e
M
F
R
S
Hi-Z
:
t
e
c
v
e
i
Table 4. Alarm Match Bit Examples
B
r
t
i
Seconds Minutes Hours Date Months Alarm condition
a
D
1
0
0
0
0
1
1
1
1
1
1
1
1
No match required = alarm 1/second
n
r
1
Alarm when seconds match = alarm 1/minute
o
O
e
t
0
0
0
1
0
0
1
1
1
Alarm when seconds, minutes match = alarm 1/hour
N
l
1
0
Alarm when seconds, minutes, hours match = alarm 1/date
A
Alarm when seconds, minutes, hours, date match = alarm 1/month
Rev. 3.2
Sept. 2011
Page 7 of 22
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
