Document Number: 001-84459 Rev. *H Page 6 of 21
Slave Device Address
The first byte that the FM24V01 expects after a START condition
is the slave address. As shown in Figure 6, the slave address
contains the device type or slave ID, the device select addre ss
bits, and a bit that specifies if the transaction is a read or a write.
Bits 7-4 are the device type (slave ID) and should be set to 1010b
for the FM24V01. These bits allow other function types to reside
on the I2C bus within an identical address range. Bits 3-1 are the
device select address bits. They must match the corresponding
value on the external address pins to select the device. Up to
eight FM24V01 devices can reside on the same I2C bus by
assigning a different add ress to each. Bit 0 is the read/write bit
(R/W). R/W = ‘1’ indicates a read operation and R/W = ‘0’
indicates a write operation.
High Spee d Mode (Hs-mode)
The FM24V01 supports a 3.4-MHz high speed mo de. A master
code (00001XXXb) must be issued to place the device into high
speed mode. Communication between master and slave will
then be enabled for speeds up to 3.4-MHz. A STOP condition will
exit Hs-mode. Single- and multiple-byte reads and writes are
supported.
Addressing Overview
After the FM24V01 (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 14-bit address is latched internally. Each access
causes the latched address value to be incremented automati-
cally. 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.
After transmission of each data byte, just prior to the
acknowledge, the FM24V01 increments the internal address
latch. This allows the next sequential byte to be accessed with
no additional addressing. After the last address (3FFFh) is
reached, the address latch will roll over to 0000h. There is no
limit to th e number of bytes that can be accessed with a sin gle
read or write operation.
Data Transfer
After the address bytes have been transmitted, data transfer
between the bus master and the FM24V01 can begin. For a read
operation the FM24V01 will place 8 data bits on the bus then wait
for an acknowledge from the master. If the acknowledge occurs,
the FM24V01 will transfer the next sequential byte. If the
acknowledge is not sent, the FM24V01 will end the read
operation. For a write operation, the FM24V01 will accept 8 data
bits from the master then send an acknowledge. All data transfer
occurs MSB (most significant bit) first.
Memory Operation
The FM24V01 is designed to operate in a manner very similar to
other I2C 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 FM24V01 and a similar configuration EEPROM
during writes. The complete operation for both writes an d reads
is explained below.
Write Operation
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 3FFFh to 0000h.
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 techn ique used with EEPROMs
to determine if a write is complete is unnecessary and will always
return a ready condition.
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
Figure 6. Memory Slav e Device Address
Slave ID
10 10A2 A0A1
Device Select
Figure 7. Data transfer format in Hs-mode
handbook, full pagewidth
F/S-mode Hs-mode F/S-mode
01
/A 1 DATA
n (bytes + ack.)
W/R
S
MASTER CODE S SLAVE ADD.
Hs-mode continues
SSLAVE ADD.
P
No Acknowledge
Acknowledge or
No Acknowledge