AD8155ACPZ-R7 datasheet(25/35 Pages) AD

25 / 35 page

Data Sheet

AD8155

Rev. A | Page 25 of 35

I2C INTERFACE DATA TRANSFERS: DATA READ

To read data from the AD8155 register set, a microcontroller or

any other I2C master must send the appropriate control signals

to the AD8155 slave device. The following steps must be taken,

where the signals are controlled by the I2C master, unless other-

wise specified. For a diagram of the procedure, see Figure 42.

Send a start condition (while holding the SCL line high,

pull the SDA line low).

Send the AD8155 part address (seven bits) whose upper

four bits are the static value b1010 and whose lower three

bits are controlled by the I2C_A[2:0] input pins. This

transfer should be MSB first.

Send the write indicator bit (0).

Wait for the AD8155 to acknowledge the request.

Send the register address (eight bits) from which data is to

be read. This transfer should be MSB first. The register

address is kept in memory in the AD8155 until the part is

reset or the register address is written over with the same

procedure (Step 1 to Step 6).

Wait for the AD8155 to acknowledge the request.

Send a repeated start condition (while holding the SCL line

high, pull the SDA line low).

Send the AD8155 part address (seven bits) whose upper

four bits are the static value b1010 and whose lower three

bits are controlled by the I2C_A[2:0] input pins. This

transfer should be MSB first.

Send the read indicator bit (1).

10. Wait for the AD8155 to acknowledge the request.

11. The AD8155 then serially transfers the data (eight bits)

held in the register indicated by the address set in Step 5.

12. Acknowledge the data.

13. Do one or more of the following:

Send a stop condition (while holding the SCL line high,

pull the SDA line high) and release control of the bus.

Send a repeated start condition (while holding the

SCL line high, pull the SDA line low) and continue

with Step 2 of the write procedure (see the I2C

Interface Data Transfers: Data Write section) to

perform a write.

Send a repeated start condition (while holding the

SCL line high, pull the SDA line low) and continue

with Step 2 of this procedure to perform a read from

another address.

Send a repeated start condition (while holding the

SCL line high, pull the SDA line low) and continue

with Step 8 of this procedure to perform a read from

the same address.

In Figure 42, the AD8155 read process is shown. The SCL signal is

shown along with a general read operation and a specific example.

In this example, the value 0x49 is read from Address 0x6D of

an AD8155 device with a 0x53 part address. The part address

is seven bits wide and is composed of the AD8155 static upper

four bits (b1010) and the pin-programmable lower three bits

(I2C_A[2:0]). The address pins are set to b011. In Figure 42, the

corresponding step number is visible in the circle under the

waveform. The SCL line is driven by the I2C master and never

by the AD8155 slave. As for the SDA line, the data in the

shaded polygons is driven by the AD8155, whereas the data in

the nonshaded polygons is driven by the I2C master. The end

phase case shown is that of Step 13a.

It is important to note that the SDA line changes only when

the SCL line is low, except for the case of sending a start, stop,

or repeated start condition, as in Step 1, Step 7, and Step 13.

In Figure 42, A is the same as ACK. Equally, Sr represents a

repeated start where the SDA line is brought high before SCL

is raised. SDA is then dropped while SCL is still high.

SCL

SDA

13a

b1010

A Sr

DATA

STOP

START

ADDR

[2:0]

ADDR

[2:0]

b1010

Figure 42. I2C Read Diagram

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