TCA6507_16 Datasheet, PDF (18/45 Pages) Texas Instruments – Low-Voltage 7-Bit I2C and SMBus LED Driver

TCA6507
SCPS164C – MAY 2007 – REVISED JANUARY 2016
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Programming (continued)
8.5.2.2 Reads
Reading from a slave is very similar to writing, but requires some additional steps. To read from a slave, the
master must first instruct the slave which register it wishes to read from. This is done by the master starting off
the transmission in a similar fashion as the write, by sending the address with the R/W bit equal to 0 (signifying a
write), followed by the register address it wishes to read from. Once the slave acknowledges this register
address, the master sends a START condition again, followed by the slave address with the R/W bit set to 1
(signifying a read). This time, the slave acknowledges the read request, and the master releases the SDA bus,
but continues supplying the clock to the slave. During this part of the transaction, the master becomes the
master-receiver, and the slave becomes the slave-transmitter.
The master continues to send out the clock pulses, but releases the SDA line so that the slave can transmit data.
At the end of every byte of data, the master sends an ACK to the slave, letting the slave know that it is ready for
more data. Once the master has received the number of bytes it is expecting, it sends a NACK, signaling to the
slave to halt communications and release the bus. The master follows this up with a STOP condition.
Figure 16 shows an example of reading a single byte from a slave register.
Master controls SDA line
Slave controls SDA line
Read from one register in a device
Device (Slave) Address (7 bits)
Register Address 0x03 (8 bits)
Device (Slave) Address (7 bits) Data Byte from Register 0x03 (8 bits)
S 1 0 0 0 1 0 1 0 A 0 0 0 0 0 0 1 1 A Sr 1 0 0 0 1 0 1 1 A D7 D6 D5 D4 D3 D2 D1 D0 NA P
START
R/W=0 ACK
ACK Repeated START
R/W=1 ACK
Figure 16. Read From Register Example
NACK STOP
8.5.3 Device Address
The address of the TCA6507 is shown in Figure 17.
Fixed Slave Address
1
0
0
0
1
0
1 R/W
Figure 17. TCA6507 Address
The last bit of the slave address defines the operation (read or write) to be performed. High (1) selects a read
operation, and low (0) selects a write operation.
Table 2. Interface Definition
BYTE
I²C slave address
Px I/O data bus
BIT
7 (MSB)
6
5
4
3
2
1
0 (LSB)
1
0
0
0
1
0
1
R/W
X ⁽¹⁾
P6
P5
P4
P3
P2
P1
P0
(1) X = Don't care.
18
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