ADM1027 datasheet(9/56 Pages) AD

9 / 56 page

REV. A

ADM1027

–9–

Any number of bytes of data can be transferred over the serial

bus in one operation. However, it is not possible to mix read

and write in one operation because the type of operation is

determined at the beginning and subsequently cannot be changed

without starting a new operation.

In the case of the ADM1027, write operations contain either

one or two bytes, and read operations contain one byte and

perform the following functions:

To write data to one of the device data registers or read data

from it, the address pointer register must be set so the correct

data register is addressed, then data can be written into that

contains an address that is stored in the address pointer register.

If data is to be written to the device, then the write operation

contains a second data byte that is written to the register selected

by the address pointer register.

This is illustrated in Figure 6. The device address is sent over

the bus followed by R/W being set to 0. This is followed by two

data bytes. The first data byte is the address of the internal data

internal data register.

When reading data from a register, there are two possibilities:

1. If the ADM1027 address pointer register value is unknown or

not the desired value, it is first necessary to set it to the correct

value before data can be read from the desired data register.

This is done by performing a write to the ADM1027 as before,

but only sending the data byte containing the register address,

as data is not to be written to the register. This is shown in

Figure 7.

A read operation is then performed consisting of the serial

bus address, R/W bit set to 1, followed by the data byte read

from the data register. This is shown in Figure 8.

2. If the address pointer register is known to be already at the

desired address, data can be read from the corresponding data

so Figure 7 can be omitted.

R/W

SCL

SDA

ACK. BY

ADM1027

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS

BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY

ADM1027

ACK. BY

ADM1027

STOP BY

MASTER

FRAME 3

DATA

BYTE

SCL (CONTINUED)

SDA (CONTINUED)

Figure 6. Writing a Register Address to the Address Pointer Register, Then Writing Data to the Selected Register

R/W

SCL

SDA

ACK. BY

ADM1027

STOP BY

MASTER

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS

BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

ACK. BY

ADM1027

Figure 7. Writing to the Address Pointer Register Only

R/W

SCL

SDA

NO ACK. BY

MASTER

STOP BY

MASTER

START BY

MASTER

FRAME 1

SERIAL BUS ADDRESS

BYTE

FRAME 2

DATA BYTE FROM ADM1027

ACK. BY

ADM1027

Figure 8. Reading Data from a Previously Selected Register

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