ADT7468 Analog Devices, Inc., ADT7468 Datasheet - Page 13

• Manufacturer Part Number: ADT7468
• Description: Dbcool Remote Thermal Controller And Voltage Monitor
• Manufacturer: Analog Devices, Inc.

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. However, 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.
In addition to supporting the send byte and receive byte
protocols, the ADT7468 also supports the read byte protocol.
(See Intel’s System Management Bus Specifications Rev. 2 for
more information.)
If several read or write operations must be performed in
succession, the master can send a repeat start condition instead
of a stop condition to begin a new operation.
WRITE OPERATIONS
The SMBus specification defines several protocols for different
types of read and write operations. The ones used in the
ADT7468 are discussed below. The following abbreviations are
used in the diagrams:
S: START
P: STOP
R: READ
W: WRITE
A: ACKNOWLEDGE
A : NO ACKNOWLEDGE
The ADT7468 uses the following SMBus write protocols.
Send Byte
In this operation, the master device sends a single command
byte to a slave device as follows:
SDA
SCL
SDA
SCL
START BY
MASTER
START BY
MASTER
0
1
1
0
1
1
SERIAL BUS ADDRESS BYTE
SERIAL BUS ADDRESS BYTE
0
0
1
FRAME 1
1
FRAME 1
1
1
Figure 18. Reading Data from a Previously Selected Register
Figure 17. Writing to the Address Pointer Register Only
1
1
0
0
R/W
R/W
Rev. A | Page 13 of 84
ADT7468
ACK. BY
ADT7468
ACK. BY
9
9
D7
D7
1
1
1.
2.
3.
4.
5.
6.
For the ADT7468, the send byte protocol is used to write a
register address to RAM for a subsequent single byte read from
the same address. This operation is illustrated in Figure 19.
If the master is required to read data from the register
immediately after setting up the address, it can assert a repeat
start condition immediately after the final ACK and carry out a
single byte read without asserting an intermediate stop
condition.
D6
D6
ADDRESS POINTER REGISTER BYTE
The master device asserts a start condition on SDA.
The master sends the 7-bit slave address followed by the
write bit (low).
The addressed slave device asserts ACK on SDA.
The master sends a command code.
The slave asserts ACK on SDA.
The master asserts a stop condition on SDA and the
transaction ends.
D5
D5
Figure 19. Setting a Register Address for a Subsequent Read
DATA BYTE FROM ADT7468
D4
D4
FRAME 2
S
1
FRAME 2
D3
ADDRESS
D3
SLAVE
2
D2
D2
W A
D1
D1
3
REGISTER
ADDRESS
D0
D0
NO ACK. BY
4
MASTER
ADT7468
ACK. BY
9
9
A
5
P
6
STOP BY
MASTER
STOP BY
MASTER
ADT7468