REV. 0

ADM1020

–9–

In the case of the ADM1020, write operations contain ei-

ther one or two bytes, while 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 that the

correct data register is addressed, then data can be written

into that register or read from it. The first byte of a write

operation always contains a valid 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 12a. The device address is sent over

the bus followed by R/

W set to 0. This is followed by two data

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

register to be written to, which is stored in the Address Pointer

Register. The second data byte is the data to be written to the

internal data register.

When reading data from a register there are two possibilities:

1. If the ADM1020's Address Pointer Register value is un-

known 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

ADM1020 as before, but only the data byte containing the

register read address is sent, as data is not to be written to

the register. This is shown in Figure 12b.

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 12c.

2. If the Address Pointer Register is known to be already at the

desired address, data can be read from the corresponding

data register without first writing to the Address Pointer

Register, so Figure 12b can be omitted.

NOTES

1. Although it is possible to read a data byte from a data register

without first writing to the Address Pointer Register, if the

Address Pointer Register is already at the correct value, it is

not possible to write data to a register without writing to the

Address Pointer Register, because the first data byte of a

write is always written to the Address Pointer Register.

2. Don't forget that the ADM1020 registers have different ad-

dresses for read and write operations. The write address of a

register must be written to the address pointer if data is to be

written to that register, but it is not possible to read data

from that address. The read address of a register must be

written to the address pointer before data can be read from

that register.

R/

W

A6

SCLK

SDATA

A5

A4

A3

A2

A1

A0

D7

D6

D5

D4

D3

D2

D1

D0

ACK. BY

ADM1020

START BY

MASTER

19

1

ACK. BY

ADM1020

9

D7

D6

D5

D4

D3

D2

D1

D0

ACK. BY

ADM1020

STOP BY

MASTER

1

9

SCL (CONTINUED)

SDA (CONTINUED)

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 3

DATA BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

Figure 12a. Writing a Register Address to the Address Point Register, then Writing Data to the Selected Register

R/

W

A6

SCLK

SDATA

A5

A4

A3

A2

A1

A0

D7

D6

D5

D4

D3

D2

D1

D0

ACK. BY

ADM1020

STOP BY

MASTER

START BY

MASTER

19

1

ACK. BY

ADM1020

9

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

Figure 12b. Writing to the Address Pointer Register Only

R/

W

A6

SCLK

SDATA

A5

A4

A3

A2

A1

A0

D7

D6

D5

D4

D3

D2

D1

D0

NO ACK.

BY MASTER

STOP BY

MASTER

START BY

MASTER

19

1

ACK. BY

ADM1020

9

FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

DATA BYTE FROM ADM1020

Figure 12c. Reading Data from a Previously Selected Register