FM31278/276/274/272 - 5V I2C Companion
A1, A0
SCL
SDA
2-Wire
Interface
LockOut
F-RAM
Array
LockOut
RST
Watchdog
LV Detect
Special
Function
Registers
S/N
RTC Cal.
RTC Registers
X1
PFI
+
CAL/PFO
-
2.5V
1.2V
RTC
X2
512Hz
Event
Counters
CNT1
CNT2
-
+
VDD
Switched Power
VBAK
Nonvolatile
Battery Backed
Figure 1. Block Diagram
Pin Descriptions
Pin Name
A0, A1
CNT1, CNT2
CAL/PFO
X1, X2
/RST
SDA
Type
Input
Input
Output
I/O
I/O
I/O
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 these pins are not used.
In calibration mode, this pin supplies a 512 Hz square-wave output for clock
calibration. In normal operation, this is the early power-fail output.
32.768 kHz crystal connection. When using an external oscillator, apply the clock to
X1 and a DC mid-level to X2 (see Crystal Oscillator section for suggestions).
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
part on the falling edge, and in 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 ground and the VBC bit should be cleared.
Supply Voltage
Ground
SCL
PFI
VBAK
VDD
VSS
Input
Input
Supply
Supply
Supply
Rev. 2.0
Dec. 2007
Page 3 of 25
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
