RAMTRON FM1608 User Manual

FM1608

64Kb Bytewide FRAM Memory

Features

64K bit Ferroelectric Nonvolatile RAM

• Organized as 8,192 x 8 bits

• High Endurance 1 Trillion (1 0

12

) Read/Writes

• 45 year Data Retention

• NoDelay™ Writes

• Advanced High-Reliability Ferroelectric Process

Superior to BBSRAM Modules

• No battery concerns

• Monolithic reliability

• True surface mount solution, no rework steps

• Superior for moisture, shock, and vibration

• Resistant to negative voltage und e rshoots

Description

The FM1608 is a 64-kilobit nonvolatile memory
employing an advanced ferroelectric process. A
ferroelectric random access memory or FRAM is
nonvolatile but operates in o ther respects as a RAM.
It provides data retention for 45 years while
eliminating the reliability concerns, functional
disadvantages and system design complexities of
battery-backed SRAM. Its fast write and high write
endurance make it superior to other types of
nonvolatile memory.

In-system operation of the FM1608 is very similar to
other RAM based devices. Minimum read- and write­cycle times are equal. The FRAM memory, however,
is nonvolatile due to its unique ferroelectric memory
process. Unlike BBSRAM, the FM1608 is a truly
monolithic nonvolatile memory. It provides the same
functional benefits of a fast write without the serious
disadvantages associated with modules and batteries
or hybrid memory solutions.

These capabilities make the FM1608 ideal for
nonvolatile memory applications requiring frequent
or rapid writes in a bytewide environment. The
availability of a true surface-mount package improves
the manufacturability of new designs, while the DIP
package facilitates simple design retrofits. The
FM1608 offers guaranteed operation over an
industrial temperature range of -40°C to +85°C.

SRAM & EEPROM Compatible

• JEDEC 8Kx8 SRAM & EEPROM pinout

• 120 ns Access Time

• 180 ns Cycle Time

Low Power Operation

• 15 mA Active Current

• 20 µA Standby Current

Industry Standard Configurat ion

• Industrial Temperature -40° C to +85° C

• 28-pin SOIC or DIP

• “Green”/RoHS Packaging

Pin Configuration

NC

A12

A7
A6
A5
A4
A3
A2
A1

A0
DQ0
DQ1
DQ2
VSS

1
2
3
4
5
6
7
8

9
10
11
12
13
14

28
27
26
25
24
23
22
21
20
19
18
17
16
15

VDD
WE
NC
A8
A9
A11
OE
A10
CE
DQ7
DQ6
DQ5
DQ4
DQ3

Ordering Information

FM1608-120-PG 120 ns access, 28-pin “Green” DIP
FM1608-120-SG 120 ns access, 28-pin “Green” SOIC

This product conforms to specifications per the terms of the Ramtron Ramtron International Corporation
standard warranty. The product has completed Ramtron’s internal 1850 Ramtron Drive, Colorado Springs, CO 80921
qualification testing and has reached production status. (800) 545-FRAM, [phone]
http://www.ramtron.com

Rev. 3.2
May 2007 1 of 12

FM1608

CE

WE

OE

A0-A12

Address

Latch

Control

Logic

A10-A12

A0-A7

A8-A9

Row

Decoder

Block Decoder

8,192 x 8 FRAM Array

Column Decoder

I/O Latch

Bus Driver

DQ0-7

Figure 1. Block Diagram

Pin Description

Pin Name I/O Pin Description

A0-A12 Input Address: The 13 address inputs select one of 8,192 bytes in the FRAM array. The

address value will be latched on the falling edge of /CE.
DQ0-7 I/O Data: 8-bit bi-directional data bus for accessing the FRAM array.
/CE Input Chip Enable: /CE selects the device when low. Asserting /CE low causes the address

to be latched internally. Address changes that occur after /CE goes low will be

ignored until the next falling edge occurs.
/OE Input Output Enable: Asserting /OE low causes the FM1608 to drive the data bus when

valid data is available. Deasserting /OE high causes the DQ pins to be tri-stated.
/WE Input Write Enable: Asserting /WE low causes the FM1608 to write the contents of the

data bus to the address location latched by the falling edge of /CE.
VDD Supply Supply Voltage: 5V
VSS Supply Ground.

Functional Truth Table

/CE /WE Function

H X Standby/Precharge
↓

X Latch Address (and Begin Write if /WE=low)
L H Read
L

↓

Write

Note: The /OE pin controls only the DQ output buffers.

Rev. 3.2
May 2007 2 of 12

FM1608

Overview

The FM1608 is a bytewide FRAM memory. The
memory array is logically organized as 8,192 x 8 and
is accessed using an industry standard parallel
interface. The FM1608 is inherently nonvolatile via
its unique ferroelectric process. All data written to the
part is immediately nonvolatile with no delay.
Functional operation of the FRAM memory is the
same as SRAM type devices, except the FM1608
requires a falling edge of /CE to start each memory
cycle.

Memory Architecture

Users access 8,192 memory locations each with 8
data bits through a parallel interface. The 13-bit
address specifies each of the 8,192 bytes uniquely.
Internally, the memory array is organized into 8
blocks of 1Kb each. The 3 most-significant address
inputs decode one of 8 blocks. This block
segmentation has no effect on o peration, however the
user may wish to group data into blocks by its
endurance requirements as explained in a later
section.

The cycle time is the same for read and write memory
operations. This simplifies memory controller logic
and timing circuits. Likewise the access time is the
same for read and write memory operations. When
/CE is deasser ted high, a pre charge opera tion begins,
and is required of every memory cycle. Thus unlike
SRAM, the access and cycle times are not equal.
Writes occur immediately at the end of the access
with no delay. Unlike an EEPROM, it is not
necessary to poll the device for a ready condition
since writes occur at bus speed.

Note that the FM1608 has no special power-down
demands. It will not block user access, and it contains
no power-management circuits other than a simple
internal power-on reset. It is the user’s responsibility
to ensure that VDD is within datasheet tolerances and
to ensure the proper voltage level and timing
relationship between VDD and /CE in power-up and
power-down events to prevent incorrect operation.

Memory Operation

The FM1608 is designed to operate in a manner very
similar to other bytewide memory products. For users
familiar with BBSRAM, the performance is
comparable but the bytewide interface operates in a
slightly different manner as described below. For
users familiar with EEPROM, the obvious differences
result from the higher write performance

of FRAM technology including NoDelay writes and
much higher write endurance.

Read Operation

A read operation begins on the falling edge of /CE.
At this time, the address bits are latched and a
memory cycle is initiated. Once started, a complete
memory cycle must be completed internally
regardless of the state of /CE. Data becomes available
on the bus after the access time has been satisfied.

After the address has been latched, the address value
may change upon satisfying the hold time parameter.
Unlike an SRAM, changing address values will have
no effect on the memory operation after the address is
latched.

The FM1608 will drive the data bus when /OE is
asserted low. If /OE is asserted after the memory
access time has been satisfied, the data bus will be
driven with valid data. If /OE is asserted prior to
completion of the memory access, the data bus will
not be driven until valid data is available. This feature
minimizes supply current in the system by eliminating
transients caused by invalid data being driven onto
the bus. When /OE is inactive the data bus will
remain tri-stated.

Write Operation

Writes occur in the FM1608 within the same time
interval as reads. The FM1608 supports both /CE­and /WE-controlled write cycles. In both cases, the
address is latched on the falling edge of /CE.

In a /CE-controlled write, the /WE signal is asserted
prior to beginning the memory cycle. That is, /WE is
low when /CE falls. In this case, the part begins the
memory cycle as a write. The FM1608 will not drive
the data bus regardless of the state of /OE.

In a /WE-controlled write, the memory cycle begins
on the falling edge of /CE. The /WE signal falls after
the falling edge of /CE. Therefore the memory cycle
begins as a read. The data bus will be driven
according to the state of /OE until /WE falls. The
timing of both /CE- and /WE-controlled write cycles
is shown in the Electrical Specifications section.

Write access to the array begins asynchronously after
the memory cycle is initiated. The write access
terminates on the rising edge of /WE or /CE,
whichever is first. Data set-up time, as shown in the
electrical specifications, indicates the interval during
which data cannot change prior to the end of the write
access.

Rev. 3.2
May 2007 3 of 12

FM1608

Unlike other truly nonvolatile memory technologies,
there is no write delay with FRAM. Since the read
and write access times of the underlying memory are
the same, the user exp eriences no delay through the
bus. The entire memory operation occurs in a single
bus cycle. Therefore, any operation including read or
write can occur immediately following a write. Data
polling, a technique used with EEPROMs to
determine if a write is complete, is unnecessary.

Precharge Operation

The precharge operatio n is an internal condition that
prepares the memory for a new access. All memory
cycles consist of a memory access and a precharge.
The precharge is initiated by deasserting the /CE pin
high. It must remain high for at least the minimum
precharge time t

.

PC

The user dictates the beginning of this operation since
a precharge will not begin until /CE rises. However
the device has a maximum /CE low time specification
that must be satisfied.

Endurance

The FM1608 internally operates with a read and
restore mechanism. Therefore, each read and write
cycle involves a change of state. The memory
architecture is based on an array of rows and
columns. Each read or write access causes an
endurance cycle for an entire row. In the FM1608, a
row is 32 bits wide. Every 4-byte boundary marks
the beginning of a new row. Endurance can be
optimized by ensuring frequently accessed data is

located in different rows. Regardless, FRAM offers
substantially higher write endurance than other
nonvolatile memories. The rated endurance limit of

12

10

cycles will allow 3000 accesses per second to the

same row for 10 years.

FRAM Design Considerations

When designing with FRAM for the first time, users
of SRAM will recognize a few minor differences.
First, bytewide FRAM memories latch each address
on the falling edge of chip enable. This allows the
address bus to change after starting the memory
access. Since every access latches the memory
address on the falling edge of /CE, users cannot
ground it as they might with SRAM.

Users who are modifying existing designs to use
FRAM should examine the memory controller for
timing compatibility of address and control pins.
Each memory access must be qualified with a low
transition of /CE. In many cases, this is the only
change required. An example of the signal
relationships is shown in Figure 2 below. Also shown
is a common SRAM signal relationship that will not
work for the FM1608.

The reason for /CE to strobe for each address is two­fold: it latches the new address and creates the
necessary precharge period while /CE is high.

Figure 2. Memory Address and /CE Relationships

Rev. 3.2
May 2007 4 of 12