TCA9548A_15 Datasheet, PDF (14/35 Pages) Texas Instruments – Low-Voltage 8-Channel I2C Switch With Reset

TCA9548A
SCPS207E – MAY 2012 – REVISED OCTOBER 2015
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Programming (continued)
The last bit of the slave address defines the operation (read or write) to be performed. When it is high (1), a read
is selected, while a low (0) selects a write operation.
Table 1. Address Reference
INPUTS
A2
A1
A0
L
L
L
L
L
H
L
H
L
L
H
H
H
L
L
H
L
H
H
H
L
H
H
H
I²C BUS SLAVE ADDRESS
112 (decimal), 70 (hexadecimal)
113 (decimal), 71 (hexadecimal)
114 (decimal), 72 (hexadecimal)
115 (decimal), 73 (hexadecimal)
116 (decimal), 74 (hexadecimal)
117 (decimal), 75 (hexadecimal)
118 (decimal), 76 (hexadecimal)
119 (decimal), 77 (hexadecimal)
8.5.3 Bus Transactions
Data must be sent to and received from the slave devices, and this is accomplished by reading from or writing to
registers in the slave device.
Registers are locations in the memory of the slave which contain information, whether it be the configuration
information or some sampled data to send back to the master. The master must write information to these
registers in order to instruct the slave device to perform a task.
While it is common to have registers in I²C slaves, note that not all slave devices will have registers. Some
devices are simple and contain only 1 register, which may be written to directly by sending the register data
immediately after the slave address, instead of addressing a register. The TCA9548A is example of a single-
register device, which is controlled via I²C commands. Since it has 1 bit to enable or disable a channel, there is
only 1 register needed, and the master merely writes the register data after the slave address, skipping the
register number.
8.5.3.1 Writes
To write on the I²C bus, the master will send a START condition on the bus with the address of the slave, as well
as the last bit (the R/W bit) set to 0, which signifies a write. The slave will acknowledge, letting the master know it
is ready. After this, the master will start sending the control register data to the slave until the master has sent all
the data necessary (which is sometimes only a single byte), and the master will terminate the transmission with a
STOP condition.
There is no limit to the number of bytes sent, but the last byte sent is what will be in the register.
Figure 10 shows an example of writing a single byte to a slave register.
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