FM24V05 - 512Kb I2C FRAM
Memory Operation
The FM24V05 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 F-RAM
technology. These improvements result in some
differences between the FM24V05 and a similar
configuration EEPROM during writes. The complete
operation for both writes and reads is explained
below.
Device Select
Slave ID
A1
2
1
7
0
6
1
0
4
A2
3
A0
1
R/W
0
5
Figure 4. Slave Address
Write Operation
Addressing Overview
All writes begin with a slave address, then a memory
address. The bus master indicates a write operation
by setting the LSB of the slave address (R/W bit) 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 FFFFh to 0000h.
After the FM24V05 (as receiver) acknowledges the
slave address, the master can place the memory
address on the bus for a write operation. The address
requires two bytes. The complete 16-bit address is
latched internally. Each access causes the latched
address value to be incremented automatically. The
current address is the value that is held in the latch --
either a newly written value or the address following
the last access. The current address will be held for as
long as power remains or until a new value is written.
Reads always use the current address. A random read
address can be loaded by beginning a write operation
as explained below.
Unlike other nonvolatile memory technologies, there
is no effective write delay with F-RAM. 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 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 ready condition.
After transmission of each data byte, just prior to the
acknowledge, the FM24V05 increments the internal
address latch. This allows the next sequential byte to
be accessed with no additional addressing. After the
last address (FFFFh) is reached, the address latch will
roll over to 0000h. There is no limit to the number of
bytes that can be accessed with a single read or write
operation.
Internally, an actual memory 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 start or stop condition prior
to the 8th data bit. The FM24V05 uses no page
buffering.
Data Transfer
After the address information has been transmitted,
data transfer between the bus master and the
FM24V05 can begin. For a read operation the
FM24V05 will place 8 data bits on the bus then wait
for an acknowledge from the master. If the
acknowledge occurs, the FM24V05 will transfer the
next sequential byte. If the acknowledge is not sent,
the FM24V05 will end the read operation. For a write
operation, the FM24V05 will accept 8 data bits from
the master then send an acknowledge. All data
transfer occurs MSB (most significant bit) first.
The memory array can be write-protected using the
WP pin. This feature is available only on FM24V05
and FM24VN05 devices. Setting the WP pin to a
high condition (VDD) will write-protect all addresses.
The FM24V05 will not acknowledge data bytes that
are written to protected addresses. In addition, the
address counter will not increment if writes are
attempted to these addresses. Setting WP to a low
state (VSS) will deactivate this feature. WP is pulled
down internally.
Figures 5 and 6 below illustrate a single-byte and
multiple-byte write cycles.
Rev. 1.1
Feb. 2009
Page 5 of 15
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
