X24012
DEVICE ADDRESSING
Following the start condition, the X24012 monitors the SDA
bus comparing the slave address being transmit-
Following a start condition the master must output the
address of the slave it is accessing. The most significant
ted with its slave address (device type and state of A0, A1
and A2 inputs). Upon a correct compare the X24012
four bits of the slave address are the device type
identifier (see Figure 4). For the X24012 this is fixed as
1010[B].
outputs an acknowledge on the SDA line. Depending on the
state of the R/W bit, the X24012 will execute a read
or write operation.
Figure 4. Slave Address
WRITE OPERATIONS
DEVICE TYPE
IDENTIFIER
Byte Write
For a write operation, the X24012 requires a second
address field. This address field is the word address,
1
0
1
0
A2
A1
A0 R/W
comprised of eight bits, providing access to any one of the
128 words of memory. Note: the most significant bit
DEVICE
ADDRESS
is a don’t care. Upon receipt of the word address the
X24012 responds with an acknowledge, and awaits the
3847 FHD F08
next eight bits of data, again responding with an ac-
knowledge. The master then terminates the transfer by
The next three significant bits address a particular device.
A system could have up to eight X24012 devices
on the bus (see Figure 10). The eight addresses are defined
by the state of the A0, A1 and A2 inputs.
generating a stop condition, at which time the X24012 begins
the internal write cycle to the nonvolatile memory.
While the internal write cycle is in progress the X24012
inputs are disabled, and the device will not respond to
any requests from the master. Refer to Figure 5 for the
address, acknowledge and data transfer sequence.
The last bit of the slave address defines the operation to be
performed. When set to one a read operation is
selected, when set to zero a write operation is selected.
Figure 5. Byte Write
S
T
S
T
SLAVE
ADDRESS
WORD
ADDRESS
BUS ACTIVITY:
MASTER
A
R
T
DATA
O
P
SDA LINE
SDA LINE
S
P
A
C
K
A
C
K
A
C
K
BUS ACTIVITY:
X24012
BUS ACTIVITY:
X24012
3847 FHD F09
Figure 6. Page Write
S
T
A
R
T
S
T
SLAVE
ADDRESS
BUS ACTIVITY:
BUS
MASTER
WORD ADDRESS n
DATA n
DATA n–1
DATA n+3
MASTER
O
P
SDA LINE
SDA LINE
S
P
A
C
K
A
C
K
A
C
K
A
C
K
A
C
K
BUS ACTIVITY:
BUS ACTIVITY:
X24012
X24012
3847 FHD F10
NOTE: In this example n = xxxx 0000 (B); x = 1 or 0
5
ICMIC [ IC MICROSYSTEMS ]
