X24164
DEVICE ADDRESSING
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.
Following a start condition the master must output the
address of the slave it is accessing. The most significant
bitoftheslaveisaone(seeFigure4). Thenextthreebits
are the device select bits. A system could have up to
eight X24164’s on the bus. The eight addresses are
definedbythestateoftheS0, S1, andS2 inputs. S1 ofthe
slave address must be the inverse of the S1 input pin.
Following the start condition, the X24164 monitors the
SDA bus comparing the slave address being transmit-
ted with its slave address device type identifier. Upon a
correct compare the X24164 outputs an acknowledge
on the SDA line. Depending on the state of the R/W bit,
the X24164 will execute a read or write operation.
Figure 4. Slave Address
WRITE OPERATIONS
Byte Write
HIGH
ORDER
DEVICE
SELECT
WORD
ADDRESS
For a write operation, the X24164 requires a second
address field. This address field is the word address,
comprised of eight bits, providing access to any one of
2048 words in the array. Upon receipt of the word
address the X24164 responds with an acknowledge,
and awaits the next eight bits of data, again responding
with an acknowledge. The master then terminates the
transferbygeneratingastopcondition,atwhichtimethe
X24164 begins the internal write cycle to the nonvolatile
memory. While the internal write cycle is in progress the
X24164 inputs are disabled, and the device will not
respond to any requests from the master. Refer to
Figure5fortheaddress, acknowledgeanddatatransfer
sequence.
1
S
S
1
S
0
A2
A1
A0 R/W
2
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Thenextthreebitsoftheslaveaddressareanextension
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 2048 x 8 array.
Figure 5. Byte Write
S
T
S
SLAVE
ADDRESS
WORD
ADDRESS
A
R
T
T
BUS ACTIVITY:
MASTER
DATA
O
P
SDA LINE
S
P
A
C
K
A
C
K
A
C
K
BUS ACTIVITY:
X24164
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5
XICOR [ XICOR INC. ]
