FM31T372/374/376/378-G

Rev. 1.1

Apr. 2011

Page 3 of 26

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

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.

/INT

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

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.

FOUT

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

I/O

Active low reset output with weak pull-up. Also input for manual reset.

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 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.

PFI

Input

Early Power-fail Input: Typically connected to an unregulated power supply to detect an early

power failure. This pin should not be left floating.

VBAK

Supply

Backup supply voltage: A 3V battery or a large value capacitor. If no backup supply is used, this

VDD

Supply

Supply Voltage

F-RAM

Array

2-Wire

Interface

SCL

SDA

RST

A1, A0

CAL/PFO

PFI

VDD

VBAK

Temperature

Compensated

RTC

~2.4V

-

+

RTC Registers

Event

Counters

CNT1

CNT2

Special

Function

Registers

S/N

FOUT

/INT

LockOut

LockOut

+

-

1.2V

Watchdog

LV Detect

Switched Power

512Hz

Battery Backed

Nonvolatile

32.768

kHz

Temp

Sensor