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
3849 FHD F06
Figure 2. Definition of Start and Stop
SCL
SDA
START BIT
STOP BIT
3849 FHD F07
3
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