X4045 INTERSIL [Intersil Corporation], X4045 Datasheet - Page 10

• Manufacturer Part Number: X4045
• Description: CPU Supervisor with 4kbit EEPROM
• Manufacturer: INTERSIL [Intersil Corporation]

SERIAL INTERFACE
Serial Interface 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
called the master and the device being controlled is
called the slave. The master always initiates data
Figure 6. Valid Data Changes on the SDA Bus
Serial Start Condition
All commands are preceded by the start condition,
which is a HIGH to LOW transition of SDA when SCL
is 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. See Figure 7.
Figure 7. Valid Start and Stop Conditions
Serial Acknowledge
Acknowledge is a software convention used to indi-
cate successful data transfer. The transmitting device,
either master or slave, will release the bus after trans-
mitting 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 8.
The device will respond with an acknowledge after
recognition of a start condition and if the correct device
identifier and select bits are contained in the slave
address byte. If a write operation is selected, the
device will respond with an acknowledge after the
receipt of each subsequent eight bit word. The device
SDA
SCL
SDA
SCL
10
Data Stable
Start
X4043, X4045
Data Change
transfers, and provides the clock for both transmit and
receive operations. Therefore, the devices in this fam-
ily operate as slaves in all applications.
Serial Clock and Data
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. See
Figure 6.
Serial 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 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. See Figure 6.
will acknowledge all incoming data and address bytes,
except for the slave address byte when the device
identifier and/or select bits are incorrect.
In the read mode, the device will transmit eight bits of
data, release the SDA line, then monitor the line for an
acknowledge. If an acknowledge is detected and no
stop condition is generated by the master, the device
will continue to transmit data. The device will terminate
further data transmissions if an acknowledge is not
detected. The master must then issue a stop condition
to return the device to standby mode and place the
device into a known state.
Data Stable
Stop
March 16, 2006
FN8118.2