FM24C04B
Memory Operation
The FM24C04B is designed to operate in a manner
very similar to other 2-wire interface memory
products. The major differences result from the
higher performance write capability of FRAM
technology. These improvements result in some
differences between the FM24C04B and a similar
configuration EEPROM during writes. The complete
operation for both writes and reads is explained
below.
Figure 4. Slave Address
No word address occurs for a read operation. Reads
always use the lower 8-bits that are held internally in
the address latch and the 9th address bit is part of the
slave address. Reads always begin at the address
following the previous access. A random read address
can be loaded by doing a write operation as explained
below.
Write Operation
All writes begin with a slave address then a word
address. The bus master indicates a write operation
by setting the LSB of the Slave address to a 0. After
addressing, the bus master sends each byte of data to
the memory and the memory generates an
acknowledge condition. Any number of sequential
bytes may be written. If the end of the address range
is reached internally, the address counter will wrap
from 1FFh to 000h.
After transmission of each data byte, just prior to the
acknowledge, the FM24C04B increments the internal
address latch. This allows the next sequential byte to
be accessed with no additional addressing. After the
last address (1FFh) is reached, the address latch will
roll over to 000h. There is no limit to the number of
bytes that can be accessed with a single read or write
operation.
Unlike other nonvolatile memory technologies, there
is no write delay with FRAM. The entire memory
cycle occurs in less time than a single bus clock.
Therefore any operation including read or write can
occur immediately following a write. Acknowledge
polling, a technique used with EEPROMs to
determine if a write is complete is unnecessary and
will always return a done condition.
Data Transfer
After all address information has been transmitted,
data transfer between the bus master and the
FM24C04B can begin. For a read operation the
FM24C04B will place 8 data bits on the bus then wait
for an acknowledge. If the acknowledge occurs, the
next sequential byte will be transferred. If the
acknowledge is not sent, the read operation is
concluded. For a write operation, the FM24C04B will
accept 8 data bits from the master then send an
acknowledge. All data transfer occurs MSB (most
significant bit) first.
An actual memory array write occurs after the 8th
data bit is transferred. It will be complete before the
acknowledge is sent. Therefore if the user desires to
abort a write without altering the memory contents,
this should be done using a start or stop condition
prior to the 8th data bit. The FM24C04B needs no
page buffering.
Pulling write protect high will disable writes to the
entire array. The FM24C04B will not acknowledge
data bytes that are written when write protect is
asserted. In addition, the address counter will not
increment if writes are attempted. Pulling WP low
(VSS) will deactivate this feature.
Figures 5 and 6 below illustrate both a single-byte
and multiple- byte write cases.
Rev. 1.3
Feb. 2011
Page 5 of 12
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
