
Ramtron 
FM1608 
28 July 2000 
3/12 
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 similar 
to SRAM type devices. The major operating 
difference between the FM1608 and an SRAM  
(beside nonvolatile storage) is that the FM1608 
latches the address on the falling edge of /CE.  
Memory Architecture 
Users access 8,192 memory locations each with 8 data 
bits through a parallel interface. The complete address 
of 13-bits 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 lines 
decode one of 8 blocks. This block segmentation has 
no effect on operation, however the user may wish to 
group data into blocks by its endurance requirements 
as explained in a later section.  
The access and cycle time are the same for read and 
write memory operations. 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. A 
pre-charge operation, where /CE goes inactive, is a 
part of every memory cycle. Thus unlike SRAM, the 
FM1608 access and cycle times are not equal.  
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 data sheet tolerances 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 to a low state. 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 due to invalid data. When /OE is inactive 
the data bus will remain tri-stated.  
Write Operation 
Writes occur in the FM1608 in the same time interval 
as reads. The FM1608 supports both /CE and /WE 
controlled write cycles. In all 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.  
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.  
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 experiences no delay through the bus. 
The entire memory operation occurs in a single bus