Frame 1 Two-Wire Slave Address Byte

(1)

Frame 2 Data MSByte

(2)

1

Start By

Master

ACK By

INA231

ACK By

Master

From

INA231

1

9

1

9

SDA

SCL

0

0

A3

D15 D14

D13

D12

D11

D10

D9

D8

A2

A1

A0

Frame 3 Data LSByte

(2)

Stop

No ACK By

(3)

Master

From

INA231

1

9

D7

D6

D5

D4

D3

D2

D1

D0

Frame 1 Two-Wire Slave Address Byte

(1)

Frame 2 Register Pointer Byte

Start By

Master

ACK By

INA231

ACK By

INA231

1

9

1

ACK By

INA231

1

D15 D14

D13

D12

D11

D10

D9

D8

9

9

SDA

SCL

1

0

0

A3

A2

A1

A0

P7

P6

P5

P4

P3

P2

P1

P0

Frame 4 Data LSByte

Frame 3 Data MSByte

ACK By

INA231

Stop By

Master

1

D7

D6

D5

D4

D3

D2

D1

D0

9

INA231

SBOS644 – FEBRUARY 2013

www.ti.com

WRITING TO/READING FROM THE INA231

Accessing a specific register on the INA231 is accomplished by writing the appropriate value to the register

pointer. Refer to Table 2 for a complete list of registers and corresponding addresses. The value for the register

pointer (shown in Figure 27) is the first byte transferred after the slave address byte with the R/W bit low. Every

write operation to the INA231 requires a value for the register pointer.

Writing to a register begins with the first byte transmitted by the master. This byte is the slave address, with the

R/W bit low. The INA231 then acknowledges receipt of a valid address. The next byte transmitted by the master

is the address of the register that data are written to. This register address value updates the register pointer to

the desired register. The next two bytes are written to the register addressed by the register pointer. The INA231

acknowledges receipt of each data byte. The master may terminate data transfer by generating a start or stop

condition.

When reading from the INA231, the last value stored in the register pointer by a write operation determines

which register is read during a read operation. To change the register pointer for a read operation, a new value

must be written to the register pointer. This write is accomplished by issuing a slave address byte with the R/W

bit low, followed by the register pointer byte. No additional data are required. The master then generates a start

condition and sends the slave address byte with the R/W bit high to initiate the read command. The next byte is

transmitted by the slave and is the most significant byte of the register indicated by the register pointer. This byte

is followed by an ACK from the master; then the slave transmits the least significant byte. The master

acknowledges receipt of the data byte. The master may terminate data transfer by generating a Not-

Acknowledge bit (No ACK) after receiving any data byte, or generating a start or stop condition. If repeated reads

from the same register are desired, it is not necessary to continually send the register pointer bytes; the INA231

retains the register pointer value until it is changed by the next write operation.

Figure 24 and Figure 25 show the write and read operation timing diagrams, respectively. Note that register

bytes are sent most-significant byte first, followed by the least significant byte.

(1)

The value of the slave address byte is determined by the settings of the A0 and A1 pins. Refer to Table 7.

Figure 24. Timing Diagram for Write Word Format

(1)

The value of the slave address byte is determined by the settings of the A0 and A1 pins. Refer to Table 7.

(2)

Read data are from the last register pointer location. If a new register is desired, the register pointer must be updated.

See Figure 27.

(3)

ACK by Master can also be sent.

Figure 25. Timing Diagram for Read Word Format

26

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