X24325
DEVICE ADDRESSING
Following a start condition the master must output the
address of the slave it is accessing (see Figure 4). The
next three bits are the device select bits. A system
could have up to eight X24325’s on the bus. The eight
addresses are defined by the state of the S
0
, S
1
and
S
2
inputs. S
0
and S
2
of the slave address must be the
inverse of the S
0
and S
2
input pins.
Figure 4. Slave Address
HIGH ORDER
WORD
ADDRESS
The last bit of the slave address defines the operation to
be performed. When set HIGH a read operation is
selected, when set LOW a write operation is selected.
Following the start condition, the X24325 monitors the
SDA bus comparing the slave address being transmitted
with its slave address device type identifier. Upon a
correct compare the X24325 outputs an acknowledge on
the SDA line. Depending on the state of the R/W bit, the
X24325 will execute a read or write operation.
WRITE OPERATIONS
Byte Write
For a write operation, the X24325 requires a second ad-
dress field. This address field is the word address, com-
prised of eight bits, providing access to any one of 4096
words in the array. Upon receipt of the word address, the
X24325 responds with an acknowledge and awaits the
next eight bits of data, again responding with an acknowl-
edge. The master then terminates the transfer by gener-
ating a stop condition, at which time the X24325 begins
the internal write cycle to the nonvolatile memory. While
the internal write cycle is in progress the X24325 inputs
are disabled, and the device will not respond to any re-
quests from the master. Refer to Figure 5 for the address,
acknowledge and data transfer sequence.
DEVICE
SELECT
S2
S1
S0
A11
A10
A9
A8
R/W
6552 ILL F07.2
The next four bits of the slave address are an exten-
sion of the array’s address and are concatenated with
the eight bits of address in the word address field,
providing direct access to the whole 4096 x 8 array.
Figure 5. Byte Write
S
T
A
R
T
S
A
C
K
A
C
K
A
C
K
6552 ILL F08
BUS ACTIVITY:
MASTER
SDA LINE
BUS ACTIVITY:
X24325
SLAVE
ADDRESS
WORD
ADDRESS
DATA
S
T
O
P
P
5
XICOR [ XICOR INC. ]
