X24257 Datasheet, PDF (3/19 Pages) Xicor Inc. – 400kHz 2-Wire Serial EEPROM with Block Lock

X24257 – Preliminary Information
DEVICE OPERATION
Clock and Data Conventions
The device 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 pro-
vide the clock for both transmit and receive operations.
Therefore, the device will be considered a slave in all
applications.
Figure 1. Data Validity
SCL
SDA
Data Stable
Data states on the SDA line can change only during
SCL LOW. SDA state changes during SCL HIGH are
reserved for indicating start and stop conditions. Refer
to Figures 1 and 2.
Start Condition
t _{All commands are preceded by the start condition,}
which is a HIGH to LOW transition of SDA when SCL is
c HIGH. The device continuously monitors the SDA and
SCL lines for the start condition and will not respond to
any command until this condition has been met.
Produ ^Data
Figure 2. Definition of Start and Stop
Change
te ^SCL
le ^SDA
Start Bit
Stop Bit
o _{Stop Condition}
All communications must be terminated by a stop con-
s _{dition, which is a LOW to HIGH transition of SDA when}
SCL is HIGH. The stop condition is also used to place
the device into the standby power mode after a read
b _{sequence. A stop condition can only be issued after}
O ^{the transmitting device has released the bus.}
The device will respond with an acknowledge after rec-
ognition of a start condition and its slave address. If
both the device and a write operation have been
selected, the device will respond with an acknowledge
after the receipt of each subsequent 8-bit word.
In the read mode the device will transmit eight bits of
data, release the SDA line and monitor the line for an
acknowledge. If an acknowledge is detected and no
Acknowledge
stop condition is generated by the master, the device
Acknowledge is a software convention used to indicate _{will continue to transmit data. If an acknowledge is not}
successful data transfer. The transmitting device, either _{detected, the device will terminate further data trans-}
master or slave, will release the bus after transmitting _{missions. The master must then issue a stop condition}
eight bits. During the ninth clock cycle the receiver will _{to return the device to the standby power mode and}
pull the SDA line LOW to acknowledge that it received _{place the device into a known state.}
the eight bits of data. Refer to Figure 3.
REV 1.1.1 10/15/00
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Characteristics subject to change without notice. 3 of 19