ADM1030
In the case of the ADM1030, 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 that the
correct data register is addressed; data can then be written into
that register or read from it. The first byte of a write operation
always 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 2a. 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 ADM1030’s 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 ADM1030
1
SCL
9
as before, but only the data byte containing the register address
is sent, as data is not to be written to the register. This is
shown in Figure 2b.
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 2c.
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 2b 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. In Figures 2a to 2c, the serial bus address is shown as the
default value 01011(A1)(A0), where A1 and A0 are set by
the three-state ADD pin.
3. The ADM1030 also supports the Read Byte protocol, as
described in the System Management Bus specification.
1
9
SDA
START BY
MASTER
0
1
0
1
1
A1
A0
R/W
ACK. BY
ADM1030
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1030
FRAME 1
SERIAL BUS ADDRESS BYTE
1
SCL (CONTINUED)
FRAME 2
ADDRESS POINTER REGISTER BYTE
9
SDA (CONTINUED)
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1030
STOP BY
MASTER
FRAME 3
DATA BYTE
Figure 2a. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
1
SCL
9
1
9
SDA
START BY
MASTER
0
1
0
1
1
A1
A0
R/W
ACK. BY
ADM1030
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1030
STOP BY
MASTER
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
Figure 2b. Writing to the Address Pointer Register Only
1
SCL
9
1
9
SDA
START BY
MASTER
0
1
0
1
1
A1
A0
R/W
ACK. BY
ADM1030
D7
D6
D5
D4
D3
D2
D1
D0
STOP BY
NO ACK.
BY MASTER MASTER
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
DATA BYTE FROM ADM1030
Figure 2c. Reading Data from a Previously Selected Register
–8–
REV. 0
AD [ ANALOG DEVICES ]
