FM31T372/374/376/378-G
A1, A0
SCL
SDA
2-Wire
Interface
LockOut
F-RAM
Array
LockOut
RST
Watchdog
LV Detect
Special
Function
Registers
S/N
RTC Registers
FOUT
PFI
+
CAL/PFO
-
~2.4V
1.2V
Temp
Sensor
512Hz
Temperature
Compensated
RTC
Event
Counters
32.768
kHz
/INT
CNT1
CNT2
-
+
VDD
Switched Power
VBAK
Nonvolatile
Battery Backed
Figure 1.
Pin Descriptions
Pin Name
A0, A1
Block Diagram
Type
Input
Pin Description
Device select inputs are used to address multiple memories on a serial bus. To select the device
the address value on the two pins must match the corresponding bits contained in the device
address. The device select pins are pulled down internally.
Event Counter Inputs: These battery-backed inputs increment counters when an edge is detected
on the corresponding CNT pin. The polarity is programmable. These pins should not be left
floating. Tie to ground if pins are not used.
Event Counter Driven Interrupt Output. This is a battery backed open-drain output. It goes low
for at least 100 ms upon changes on either CNT1 or CNT2 pin. This pin can be left floating if
not used.
In normal operation, this is the early power-fail output. In CAL mode, it supplies a 512 Hz
square-wave output for clock calibration.
32.768kHz Clock Output. This is a battery backed open-drain output. This pin can be disabled
by setting the FOEN bit to “0”. This pin can be left floating if not used.
Active low reset output with weak pull-up. Also input for manual reset.
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.
Serial Clock: The serial clock line for the two-wire interface. Data is clocked out of the device
on the falling edge, and into the device on the rising edge. The SCL input also incorporates a
Schmitt trigger input for noise immunity.
Early Power-fail Input: Typically connected to an unregulated power supply to detect an early
power failure. This pin should not be left floating.
Backup supply voltage: A 3V battery or a large value capacitor. If no backup supply is used, this
pin should be tied to V
DD
.
Supply Voltage
CNT1, CNT2
Input
/INT
Output
CAL/PFO
FOUT
/RST
SDA
Output
Output
I/O
I/O
SCL
Input
PFI
VBAK
VDD
Input
Supply
Supply
Rev. 1.1
Apr. 2011
Page 3 of 26
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
