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ADM1021 Datasheet(PDF) 9 Page - Analog Devices

Part No. ADM1021
Description  Low Cost Microprocessor System Temperature Monitor
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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ADM1021 Datasheet(HTML) 9 Page - Analog Devices

 
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ADM1021
–9–
REV. 0
Any number of bytes of data may be transferred over the serial
bus in one operation, but it is not possible to mix read and write
in one operation, because the type of operation is determined at
the beginning and cannot subsequently be changed without
starting a new operation.
In the case of the ADM1021, write operations contain either
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, 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 13. 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 ADM1021’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 ADM1021
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 14.
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 15.
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 14 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 ADM1021 registers have different
addresses 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
ADM1021
START BY
MASTER
19
1
ACK. BY
ADM1021
9
D7
D6
D5
D4
D3
D2
D1
D0
ACK. BY
ADM1021
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 13. Writing a Register Address to the Address Pointer 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
ADM1021
STOP BY
MASTER
START BY
MASTER
19
1
ACK. BY
ADM1021
9
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
Figure 14. Writing to the Address Pointer Register Only


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