FM31T372/374/376/378-G
F-RAM
Array
2-Wire
Interface
A1, A0
SCL
LockOut
SDA
LockOut
Special
Function
Registers
RST
Watchdog
LV Detect
RTC Registers
S/N
FOUT
PFI
Temperature
Compensated
RTC
Temp
Sensor
+
-
1.2V
CAL/PFO
512Hz
32.768
kHz
/INT
Event
-
+
~2.4V
CNT1
CNT2
Counters
VDD
Switched Power
VBAK
Battery Backed
Nonvolatile
Figure 1. Block Diagram
Pin Descriptions
Pin Name
Type Pin Description
A0, A1
Input
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.
CNT1, CNT2
/INT
Input
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.
Output 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.
CAL/PFO
FOUT
Output In normal operation, this is the early power-fail output. In CAL mode, it supplies a 512 Hz
square-wave output for clock calibration.
Output 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.
/RST
SDA
I/O
I/O
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.
SCL
Input
Input
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.
PFI
VBAK
VDD
Supply Backup supply voltage: A 3V battery or a large value capacitor. If no backup supply is used, this
pin should be tied to VDD
Supply Supply Voltage
.
Rev. 1.1
Apr. 2011
Page 3 of 26
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
