FM3135 Integrated RTC/Alarm/FRAM & Embedded Crystal
F-RAM
Array
2-Wire
SCL
SDA
Interface
LockOut
Special
RTC Registers
Function
Registers
RTC Cal.
RTC
Alarm
-
VSW
+
VDD
Alarm
Switched Power
ACS
512Hz/SQW
VBAK
Battery Backed
Nonvolatile
Figure 1. Block Diagram
Pin Descriptions
Pin Name
Type
Pin Description
ACS
Output Alarm/Calibration/SquareWave: This is an open-drain output that requires an external
pullup resistor. The alarm, calibration, and square wave functions all share this output.
In Alarm mode, this pin acts as the active-low alarm output. In Calibration mode, a 512
Hz square-wave is driven out. In SquareWave mode, the user may select a frequency of
1, 512, 4096, or 32768 Hz to be used as a continuous output. Refer to Table 3. Control
Bit Settings for ACS Pin to determine the bit settings for each mode.
SDA
I/O
Serial Data & Address: This is a bi-directional line for the two-wire interface. It is
open-drain and is intended to be wire-OR’d with other devices on the two-wire bus. The
input buffer incorporates a Schmitt trigger for noise immunity and the output driver
includes slope control for falling edges. A pull-up resistor is required.
SCL
Input
Serial Clock: The serial clock line for the two-wire interface. Data is clocked out of the
part on the falling edge, and data into the device on the rising edge. The SCL input also
incorporates a Schmitt trigger input for noise immunity.
VBAK
Supply Backup supply voltage: A 3V battery or a large value capacitor. If no backup supply is
used, this pin should be tied to VSS. The trickle charger is UL recognized and ensures no
excessive current when using a lithium battery.
VDD
VSS
Supply Supply Voltage.
Supply Ground
Rev. 1.2
Feb. 2009
Page 2 of 21
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