FM24CL16
Page
Select
Memory Operation
Slave ID
The FM24CL16 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 FM24CL16 and a similar
configuration EEPROM during writes. The complete
operation for both writes and reads is explained
below.
1
0
1
0
A2
A1
A0
R/W
Figure 4. Slave Address
Word Address
Write Operation
After the FM24CL16 (as receiver) acknowledges the
slave ID, the master will place the word address on
the bus for a write operation. The word address is the
lower 8-bits of the address to be combined with the 3-
bits of the page select to specify the exact byte to be
written. The complete 11-bit address is latched
internally.
All writes begin with a slave ID then a word address
as previously mentioned. 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 7FFh to 000h.
No word address occurs for a read operation, though
the 3-bit page select is latched internally. Reads
always use the lower 8-bits that are held internally in
the address latch. That is, 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.
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 ‘ready’ condition.
After transmission of each data byte, just prior to the
acknowledge, the FM24CL16 increments the internal
address latch. This allows the next sequential byte to
be accessed with no additional addressing. After the
last address (7FFh) is reached, the address latch will
roll over to 000h. There is no limit on the number of
bytes that can be accessed with a single read or write
operation.
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 start or stop condition
prior to the 8th data bit. The FM24CL16 needs no
page buffering.
Data Transfer
After all address information has been transmitted,
data transfer between the bus master and the
FM24CL16 can begin. For a read operation the
device 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 FM24CL16 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. Setting the WP pin to a high condition
(VDD) will write-protect all addresses. The
FM24CL16 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.
Figure 5 and 6 below illustrates both a single-byte
and multiple-byte writes.
Rev 3.3
Nov. 2005
Page 5 of 13
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
