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Preliminary Information
XP2in4071N2o Connect
1K
X24012
Serial E2PROM
128 x 8 Bit
FEATURES
2.7 to 5.5V Power Supply
Low Power CMOS
—Active Current Less Than 1 mA
—Standby Current Less Than 50 µA
Internally Organized 128 x 8
Self Timed Write Cycle
—Typical Write Cycle Time of 5 ms
2 Wire Serial Interface
—Bidirectional Data Transfer Protocol
Four Byte Page Write Operation
—Minimizes Total Write Time Per Byte
High Reliability
—Endurance: 100,000 Cycles
—Data Retention: 100 Years
DESCRIPTION
The X24012 is a CMOS 1024 bit serial E2PROM,
internally organized as one 128 x 8 bank. The X24012
features a serial interface and software protocol allow-
ing operation on a simple two wire bus. Three address
inputs allow up to eight devices to share a common two
wire bus.
Xicor E2PROMs are designed and tested for applica-
tions requiring extended endurance. Inherent data re-
tention is greater than 100 years. The X24012 is avail-
able in eight pin DIP and SOIC packages.
FUNCTIONAL DIAGRAM
(8) VCC
(4) VSS
(5) SDA
(6) SCL
(3) A2
(2) A1
(1) A0
START
STOP
LOGIC
SLAVE ADDRESS
REGISTER
+COMPARATOR
START CYCLE
CONTROL
LOGIC
LOAD
INC
WORD
ADDRESS
COUNTER
XDEC
H.V. GENERATION
TIMING
& CONTROL
E2PROM
32 X 32
R/W
DOUT
ACK
PIN
YDEC
8
CK DATA REGISTER DOUT
3847 FHD F01
© Xicor, 1991 Patents Pending
3847-1
1 Characteristics subject to change without notice

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X24012
PIN DESCRIPTIONS
Serial Clock (SCL)
The SCL input is used to clock all data into and out of the
device.
Serial Data (SDA)
SDA is a bidirectional pin used to transfer data into and
out of the device. It is an open drain output and may be
wire-ORed with any number of open drain or open
collector outputs.
An open drain output requires the use of a pull-up
resistor. For selecting typical values, refer to the Guide-
lines for Calculating Typical Values of Bus Pull-Up
Resistors graph.
Address (A0, A1, A2)
The address inputs are used to set the least significant
three bits of the seven bit slave address. These inputs
can be static or actively driven. If used statically they
must be tied to VSS or VCC as appropriate. If actively
driven, they must be driven to VSS or to VCC.
PIN CONFIGURATION
A0
A1
A2
VSS
DIP/SOIC
18
27
X24012
36
45
VCC
NC
SCL
SDA
PIN NAMES
Symbol
A0–A2
SDA
SCL
NC
VSS
VCC
3847 FHD F02
Description
Address Inputs
Serial Data
Serial Clock
No Connect
Ground
+5V
3847 PGM T01
2

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X24012
DEVICE OPERATION
The X24012 supports a bidirectional bus oriented proto-
col. The protocol defines any device that sends data
onto the bus as a transmitter, and the receiving device
as the receiver. The device controlling the transfer is a
master and the device being controlled is the slave. The
master will always initiate data transfers and provide the
clock for both transmit and receive operations. There-
fore, the X24012 will be considered a slave in all
applications.
Figure 1. Data Validity
Clock and Data Conventions
Data states on the SDA line can change only during SCL
LOW. SDA state changes during SCL HIGH are re-
served for indicating start and stop conditions. Refer to
Figures 1 and 2.
Start Condition
All commands are preceded by the start condition,
which is a HIGH to LOW transition of SDA when SCL is
HIGH. The X24012 continuously monitors the SDA and
SCL lines for the start condition and will not respond to
any command until this condition has been met.
SCL
SDA
Figure 2. Definition of Start and Stop
SCL
DATA STABLE DATA
CHANGE
SDA
START BIT
STOP BIT
3847 FHD F05
3847 FHD F06
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X24012
Stop Condition
All communications must be terminated by a stop condi-
tion, which is a LOW to HIGH transition of SDA when SCL
is HIGH. The stop condition is also used by the X24012 to
place the device into the standby power mode after a read
sequence. A stop condition can only be issued after the
transmitting device has released the bus.
Acknowledge
Acknowledge is a software convention used to indicate
successful data transfers. The transmitting device will
release the bus after transmitting eight bits. During the
ninth clock cycle the receiver will pull the SDA line LOW
to acknowledge that it received the eight bits of data.
Refer to Figure 3.
Figure 3. Acknowledge Response From Receiver
The X24012 will respond with an acknowledge after
recognition of a start condition and its slave address. If
both the device and a write operation have been se-
lected, the X24012 will respond with an acknowledge
after the receipt of each subsequent eight bit word.
In the read mode the X24012 will transmit eight bits of
data, release the SDA line and monitor the line for an
acknowledge. If an acknowledge is detected and no
stop condition is generated by the master, the X24012
will continue to transmit data. If an acknowledge is not
detected, the X24012 will terminate further data trans-
missions. The master must then issue a stop condition
to return the X24012 to the standby power mode and
place the device into a known state.
SCL FROM
MASTER
1
89
DATA
OUTPUT
FROM
TRANSMITTER
DATA
OUTPUT
FROM
RECEIVER
START
ACKNOWLEDGE 3847 FHD F07
4

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X24012
DEVICE ADDRESSING
Following a start condition the master must output the
address of the slave it is accessing. The most significant
four bits of the slave address are the device type
identifier (see Figure 4). For the X24012 this is fixed as
1010[B].
Figure 4. Slave Address
DEVICE TYPE
IDENTIFIER
1 0 1 0 A2 A1 A0 R/W
DEVICE
ADDRESS
3847 FHD F08
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.
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 the start condition, the X24012 monitors the
SDA bus comparing the slave address being transmit-
ted with its slave address (device type and state of A0,
A1 and A2 inputs). Upon a correct compare the X24012
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.
WRITE OPERATIONS
Byte Write
For a write operation, the X24012 requires a second
address field. This address field is the word address,
comprised of eight bits, providing access to any one of
the 128 words of memory. Note: the most significant bit
is a don’t care. Upon receipt of the word address the
X24012 responds with an acknowledge, and awaits the
next eight bits of data, again responding with an ac-
knowledge. The master then terminates the transfer by
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.
Figure 5. Byte Write
S
T
BBUUSSAACCTTIVIVITITYY:: A
MMAASSTTEERR
R
T
SSDDAALLININEE
S
SLAVE
ADDRESS
WORD
ADDRESS
BXBX2UU24S40S01AA12C2CTTIVIVITITYY::
AA
CC
KK
DATA
S
T
O
P
P
A
C
K
3847 FHD F09
Figure 6. Page Write
S
T
BBUUSSAACCTTIVIVITITYY: : A
MMAASSTTEERR
R
T
SSDDAALLININEE
S
BXBX2U4U2S04S1A02A1C2CTTIVIVITITYY: :
SLAVE
ADDRESS
WORD ADDRESS n
AA
CC
KK
DATA n
DATA n–1
AA
CC
KK
NOTE: In this example n = xxxx 0000 (B); x = 1 or 0
DATA n+3
S
T
O
P
P
A
C
K
3847 FHD F10
5