FM32278/276/274/272 - 5V I2C Companion

Rev. 3.0

Feb. 2009

Page 3 of 21

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.

PFO

Output

Power Fail Output: This is the early power-fail output.

/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

part on the falling edge, and in 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 pin should be tied to ground and the VBC bit should be cleared. The trickle

charger is UL recognized and ensures no excessive current when using a lithium battery.

VDD

Supply

Supply Voltage

VSS

Supply

Ground

FRAM

Array

2-Wire

Interface

SCL

SDA

RST

A1, A0

PFO

PFI

VDD

VBAK

2.5V

-

+

Special

Function

Registers

S/N

LockOut

LockOut

Watchdog

LV Detect

Switched Power

Battery Backed

Nonvolatile

Event

Counters

CNT1

CNT2

+

-

1.2V