
ADT7461
serial bus in a single read or write operation is limited only
by what the master and slave devices can handle.
3.
When all data bytes have been read or written, stop condi-
tions are established. In write mode, the master will pull the
data line high during the tenth clock pulse to assert a STOP
condition. In read mode, the master device will override
the acknowledge bit by pulling the data line high during
the low period before the ninth clock pulse. This is known
as No Acknowledge. The master will then take the data line
low during the low period before the tenth clock pulse,
then high during the tenth clock pulse to assert a STOP
condition.
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 ADT7461, write
operations contain either one or two bytes, while read opera-
tions contain one byte.
To write data to one of the device data registers or to read
data from it, the address pointer register must be set so that the
correct data register is addressed. The first byte of a write opera-
tion 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
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.
. The device address is sent over
Figure 15
Figure 15. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register
0
A6
1
9
1
A5
A4
A3
A2
A1
A0
R/W
D7
D6
D5
D4
D3
D2
D1
D0
SCLK
SDAT
9
A
START BY
MASTER
ACK. BY
ADT7461
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
FRAME 3
DATA BYTE
SCLK (CONTINUED)
SDATA (CONTINUED)
ACK. BY
ADT7461
ACK. BY
ADT7461
STOP BY
MASTER
9
1
D7
D6
D5
D4
D3
D2
D1
D0
0
SCLK
SDATA
START BY
MASTER
ACK. BY
ADT7461
ACK. BY
ADT7461
STOP BY
MASTER
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
1
9
1
A6
A5
A4
A3
A2
A1
A0
R/W
D7
D6
D5
D4
D3
D2
D1
D0
9
Figure 16. Writing to the Address Pointer Register Only
0
SCLK
SDATA
START BY
MASTER
ACK. BY
ADT7461
FRAME 1
SERIAL BUS ADDRESS BYTE
FRAME 2
DATA BYTE FROM ADT7461
ACK. BY
ADT7461
STOP BY
MASTER
1
9
1
9
A6
A5
A4
A3
A2
A1
A0
R/W
D7
D6
D5
D4
D3
D2
D1
D0
Figure 17. Reading from a Previously Selected Register
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