BQ25872 Datasheet, PDF (26/68 Pages) Texas Instruments – Battery Switch Charger

bq25872
SLUSCQ6 – OCTOBER 2016
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Feature Description (continued)
8.3.6.2 START and STOP Conditions
All transactions begin with a START (S) and can be terminated by a STOP (P). A HIGH to LOW transition on the
SDA line while SCL is HIGH defines a START condition. A LOW to HIGH transition on the SDA line when the
SCL is HIGH defines a STOP condition.
START and STOP conditions are always generated by the master. The bus is considered busy after the START
condition, and free after the STOP condition.
SDA
SDA
SCL
START
(S)
Figure 15. START and STOP Conditions
SCL
STOP
(P)
8.3.6.3 Byte Format
Every byte on the SDA line must be 8 bits long. The number of bytes to be transmitted per transfer is
unrestricted. Each byte has to be followed by an Acknowledge bit. Data is transferred with the Most Significant
Bit (MSB) first. If a slave cannot receive or transmit another complete byte of data until it has performed some
other function, it can hold the clock line SCL low to force the master into a wait state (clock stretching). Data
transfer then continues when the slave is ready for another byte of data and release the clock line SCL.
SDA
MSB
Acknowledgement signal from slave
Acknowledgement signal from receiver
S or Sr
SCL
1
2
START or Repeated START
7
8
9
ACK
1
2
Figure 16. Data Transfer on the I²C Bus
8
9
P or Sr
ACK
STOP or Repeated START
8.3.6.4 Acknowledge (ACK) and Not Acknowledge (NACK)
The acknowledge takes place after every byte. The acknowledge bit allows the receiver to signal the transmitter
that the byte was successfully received and another byte may be sent. All clock pulses, including the
acknowledge 9th clock pulse, are generated by the master.
The transmitter releases the SDA line during the acknowledge clock pulse so the receiver can pull the SDA line
LOW and it remains stable LOW during the HIGH period of this clock pulse.
When SDA remains HIGH during the ninth clock pulse, this is the Not Acknowledge signal. The master can then
generate either a STOP to abort the transfer or a repeated START to start a new transfer.
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