LM3S2739 Datasheet, PDF (514/752 Pages) List of Unclassifed Manufacturers – Microcontroller

Inter-Integrated Circuit (I²C) Interface
Figure 14-4. Complete Data Transfer with a 7-Bit Address
SDA
MSB
LSB
R/S
ACK
MSB
LSB
ACK
SCL
1
2
7
8
9
Slave address
1
2
7
8
9
Data
The first seven bits of the first byte make up the slave address (see Figure 14-5 on page 514). The
eighth bit determines the direction of the message. A zero in the R/S position of the first byte means
that the master will write (send) data to the selected slave, and a one in this position means that
the master will receive data from the slave.
Figure 14-5. R/S Bit in First Byte
MSB
LSB
R/S
Slave address
14.3.1.3
Data Validity
The data on the SDA line must be stable during the high period of the clock, and the data line can
only change when SCL is Low (see Figure 14-6 on page 514).
Figure 14-6. Data Validity During Bit Transfer on the I²C Bus
SDA
SCL
Data line ^Change
stable ^{of data}
allowed
14.3.1.4
Acknowledge
All bus transactions have a required acknowledge clock cycle that is generated by the master. During
the acknowledge cycle, the transmitter (which can be the master or slave) releases the SDA line.
To acknowledge the transaction, the receiver must pull down SDA during the acknowledge clock
cycle. The data sent out by the receiver during the acknowledge cycle must comply with the data
validity requirements described in “Data Validity” on page 514.
When a slave receiver does not acknowledge the slave address, SDA must be left High by the slave
so that the master can generate a STOP condition and abort the current transfer. If the master
device is acting as a receiver during a transfer, it is responsible for acknowledging each transfer
made by the slave. Since the master controls the number of bytes in the transfer, it signals the end
of data to the slave transmitter by not generating an acknowledge on the last data byte. The slave
transmitter must then release SDA to allow the master to generate the STOP or a repeated START
condition.
14.3.1.5
Arbitration
A master may start a transfer only if the bus is idle. It's possible for two or more masters to generate
a START condition within minimum hold time of the START condition. In these situations, an
514
July 15, 2014
Texas Instruments-Production Data