Datasheet

bq24270
bq24271
www.ti.com SLUSB10 –JUNE 2012
Figure 9. START and STOP Condition
The master then generates the SCL pulses, and transmits the 8-bit address and the read/write direction bit R/W
on the SDA line. During all transmissions, the master ensures that data is valid. A valid data condition requires
the SDA line to be stable during the entire high period of the clock pulse (see Figure 10). All devices recognize
the address sent by the master and compare it to their internal fixed addresses. Only the slave device with a
matching address generates an acknowledge (see Figure 11) by pulling the SDA line low during the entire high
period of the ninth SCL cycle. Upon detecting this acknowledge, the master knows that communication link with a
slave has been established.
Figure 10. Bit Transfer on the Serial Interface
The master generates further SCL cycles to either transmit data to the slave (R/W bit 1) or receive data from the
slave (R/W bit 0). In either case, the receiver needs to acknowledge the data sent by the transmitter. So an
acknowledge signal can either be generated by the master or by the slave, depending on which one is the
receiver. The 9-bit valid data sequences consisting of 8-bit data and 1-bit acknowledge can continue as long as
necessary. To signal the end of the data transfer, the master generates a stop condition by pulling the SDA line
from low to high while the SCL line is high (see Figure 12). This releases the bus and stops the communication
link with the addressed slave. All I
2
C compatible devices must recognize the stop condition. Upon the receipt of a
stop condition, all devices know that the bus is released, and wait for a start condition followed by a matching
address. If a transaction is terminated prematurely, the master needs sending a STOP condition to prevent the
slave I
2
C logic from remaining in an incorrect state. Attempting to read data from register addresses not listed in
this section result in FFh being read out.
Figure 11. Acknowledge on the I
2
C Bus
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