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Preliminary Information
XP2in4074N2o Connect
4K
X24042
512 x 8 Bit
Serial E2PROM
TYPICAL FEATURES
2.7V to 5.5V Power Supply
Low Power CMOS
—Active Read Current Less Than 1 mA
—Active Write Current Less Than 3 mA
—Standby Current Less Than 50 µA
Internally Organized 512 x 8
2 Wire Serial Interface
—Bidirectional Data Transfer Protocol
Sixteen Byte Page Write Mode
—Minimizes Total Write Time Per Byte
Self Timed Write Cycle
—Typical Write Cycle Time of 5 ms
High Reliability
—Endurance: 100,000 Cycles
—Data Retention: 100 Years
8 Pin Mini-DlP and 8 Pin SOIC Packages
DESCRIPTION
The X24042 is a CMOS 4,096 bit serial E2PROM,
internally organized 512 x 8. The X24042 features a
serial interface and software protocol allowing operation
on a simple two wire bus.
The X24042 is fabricated with Xicor’s advanced CMOS
Textured Poly Floating Gate Technology.
The X24042 utilizes Xicor’s proprietary Direct WriteTM
cell providing a minimum endurance of 100,000 cycles
and a minimum data retention of 100 years.
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
32 X 128
YDEC
8
CK DATA REGISTER DOUT
3849 FHD F01
© Xicor, 1991 Patents Pending
3849-1
1 Characteristics subject to change without notice

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X24042
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 Pull-Up
Resistor selection graph at the end of this data sheet.
Address (A0)
A0 is unused by the X24042, however, it must be tied to
VSS to insure proper device operation.
Address (A1, A2)
The Address inputs are used to set the appropriate bits
of the seven bit slave address. These inputs can be used
static or actively driven. If used statically they must be
tied to VSS or VCC as appropriate. If driven they must be
driven to VSS or to VCC.
PIN CONFIGURATION
A0
A1
A2
VSS
DIP/SOIC
18
27
X24042
36
45
VCC
NC
SCL
SDA
3849 FHD F02
PIN NAMES
Symbol
A0–A2
SDA
SCL
NC
VSS
VCC
Description
Address Inputs
Serial Data
Serial Clock
No Connect
Ground
Supply Voltage
3849 PGM T01
2

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X24042
DEVICE OPERATION
The X24042 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 X24042 will be considered a slave in all
applications.
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.
Figure 1. Data Validity
Start Condition
All commands are preceded by the start condition,
which is a HIGH to LOW transition of SDA when SCL is
HIGH. The X24042 continuously monitors the SDA and
SCL lines for the start condition and will not respond to
any command until this condition has been met.
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
X24042 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.
SCL
SDA
DATA STABLE DATA
CHANGE
Figure 2. Definition of Start and Stop
3849 FHD F06
SCL
SDA
START BIT
STOP BIT
3849 FHD F07
3

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X24042
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.
The X24042 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 X24042 will respond with an acknowledge
Figure 3. Acknowledge Response From Receiver
after the receipt of each subsequent eight bit word.
In the read mode the X24042 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 X24042
will continue to transmit data. If an acknowledge is not
detected, the X24042 will terminate further data trans-
missions. The master must then issue a stop condition
to return the X24042 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
3849 FHD F08
4

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X24042
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 X24042 this is fixed as
1010[B].
Figure 4. Slave Address
DEVICE TYPE
IDENTIFIER
HIGH
ORDER
WORD
ADDRESS
1 0 1 0 A2 A1 A0 R/W
DEVICE
ADDRESS
3849 FHD F09
The next two significant bits addresses a particular
device. A system could have up to four X24042 devices
on the bus (see Figure 10). The four addresses are
defined by the state of the A1 and A2 input.
The next bit of the slave address is an extension of the
array’s address and is concatenated with the eight bits
of address in the word address field, providing direct
access to the whole 512 x 8 array.
Figure 5. Byte Write
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 X24042 monitors the
SDA bus comparing the slave address being transmit-
ted with its slave address (device type and state of the
A2 and A1 inputs). Upon a correct compare the X24042
outputs an acknowledge on the SDA line. Depending on
the state of the R/W bit, the X24042 will execute a read
or write operation.
WRITE OPERATIONS
Byte Write
For a write operation, the X24042 requires a second
address field. This address field is the word address,
comprised of eight bits, providing access to any one of
the 512 words in the selected page of memory. Upon
receipt of the word address the X24042 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 condi-
tion, at which time the X24042 begins the internal write
cycle to the nonvolatile memory. While the internal write
cycle is in progress the X24042 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:
X24042
AA
CC
KK
DATA
S
T
O
P
P
A
C
K
3849 FHD F10
5