FM31278/276/274/272 - 5V I2C Companion
F-RAM
Array
2-Wire
Interface
A1, A0
SCL
LockOut
SDA
LockOut
Special
Function
Registers
RST
Watchdog
LV Detect
RTC Registers
X1
S/N
PFI
RTC Cal.
+
RTC
X2
1.2V
-
CAL/PFO
512Hz
CNT1
CNT2
Event
Counters
-
+
2.5V
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
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 these pins are not used.
CAL/PFO
X1, X2
Output 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.
I/O
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.
/RST
SDA
I/O
I/O
SCL
Input
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.
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
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.
Supply Supply Voltage
VDD
VSS
Supply Ground
Rev. 2.1
Sept. 2011
Page 3 of 26
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
