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Preliminary Information
XP2in4072N2o Connect
2K
X24022
Serial E2PROM
256 x 8 Bit
FEATURES
2.7V to 5.5V Power Supply
Low Power CMOS
—Active Current Less Than 1 mA
—Standby Current Less Than 50 µA
Internally Organized 256 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 Per Byte
—Data Retention: 100 Years
DESCRIPTION
The X24022 is a CMOS 2048 bit serial E2PROM, inter-
nally organized 256 x 8. The X24022 features a serial
interface and software protocol allowing 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 X24022 is avail-
able in eight pin DIP and SOIC packages.
FUNCTIONAL DIAGRAM
(8) VCC
(4) VSS
(5) SDA
START
STOP
LOGIC
START CYCLE
H.V. GENERATION
TIMING
& CONTROL
(6) SCL
(3) A2
(2) A1
(1) A0
SLAVE ADDRESS
REGISTER
+COMPARATOR
CONTROL
LOGIC
LOAD
INC
WORD
ADDRESS
COUNTER
R/W
DOUT
ACK
PIN
XDEC
E2PROM
64 X 32
YDEC
8
CK DATA REGISTER DOUT
3848 FHD F01
© Xicor, 1991 Patents Pending
3848-1
1 Characteristics subject to change without notice

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X24022
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
X24022
36
45
VCC
NC
SCL
SDA
3848 FHD F02
PIN NAMES
Symbol
A0–A2
SDA
SCL
NC
VSS
VCC
Description
Address Inputs
Serial Data
Serial Clock
No Connect
Ground
+5V
3848 PGM T01
2

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X24022
DEVICE OPERATION
The X24022 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.
Therefore, the X24022 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 X24022 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
DATA STABLE DATA
CHANGE
3848 FHD F06
3

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X24022
Stop Condition
All communications must be terminated by a stop con-
dition, which is a LOW to HIGH transition of SDA when
SCL is HIGH. The stop condition is also used by the
X24022 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 2. Definition of Start and Stop
The X24022 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 X24022 will respond with an acknowledge
after the receipt of each subsequent eight bit word.
In the read mode the X24022 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 X24022
will continue to transmit data. If an acknowledge is not
detected, the X24022 will terminate further data trans-
missions. The master must then issue a stop condition
to return the X24022 to the standby power mode and
place the device into a known state.
SCL
SDA
START BIT
Figure 3. Acknowledge Response From Receiver
SCL FROM
MASTER
DATA
OUTPUT
FROM
TRANSMITTER
DATA
OUTPUT
FROM
RECEIVER
START
1
STOP BIT
3848 FHD F07
89
ACKNOWLEDGE
3848 FHD F08
4

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X24022
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 X24022 this is fixed as 1010[B].
Figure 4. Slave Address
DEVICE TYPE
IDENTIFIER
1 0 1 0 A2 A1 A0 R/W
DEVICE
ADDRESS
3848 FHD F09
The next three significant bits address a particular
device. A system could have up to eight X24022 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.
Figure 5. Byte Write
Following the start condition, the X24022 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 X24022
outputs an acknowledge on the SDA line. Depending on
the state of the R/W bit, the X24022 will execute a read
or write operation.
WRITE OPERATIONS
Byte Write
For a write operation, the X24022 requires a second
address field. This address field is the word address,
comprised of eight bits, providing access to any one of
the 256 words of memory. Upon receipt of the word
address the X24022 responds with an acknowledge,
and awaits the next eight bits of data, again responding
with an acknowledge. The master then terminates the
transfer by generating a stop condition, at which time the
X24022 begins the internal write cycle to the nonvolatile
memory. While the internal write cycle is in progress the
X24022 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.
S
T
BUS ACTIVITY: A
MASTER
R
T
SLAVE
ADDRESS
WORD
ADDRESS
SDA LINE
S
BUS ACTIVITY:
X24022
AA
CC
KK
DATA
S
T
O
P
P
A
C
K
3848 FHD F10
5