Datasheet

ADM1069
Rev. C | Page 26 of 32
The device also has several identification registers (read-only)
that can be read across the SMBus. Table 12 lists these registers
with their values and functions.
Table 12. Identification Register Values and Functions
Name Address Value Function
MANID 0xF4 0x41 Manufacturer ID for Analog Devices
REVID 0xF5 0x02 Silicon revision
MARK1 0xF6 0x00 Software brand
MARK2 0xF7 0x00 Software brand
General SMBus Timing
Figure 36, Figure 37, and Figure 38 are timing diagrams for
general read and write operations using the SMBus. The SMBus
specification defines specific conditions for different types of
read and write operations, which are discussed in the Wr ite
Operations and Read Operations sections.
The general SMBus protocol operates as follows:
Step 1
The master initiates data transfer by establishing a start condition,
defined as a high-to-low transition on the serial data line SDA,
while the serial clock line SCL remains high. This indicates that
a data stream follows. All slave peripherals connected to the serial
bus respond to the start condition and shift in the next eight bits,
consisting of a 7-bit slave address (MSB first) plus an R/
W
bit.
This bit determines the direction of the data transfer, that is,
whether data is written to or read from the slave device (0 = write,
1 = read).
The peripheral whose address corresponds to the transmitted
address responds by pulling the data line low during the low period
before the ninth clock pulse, known as the acknowledge bit, and
by holding it low during the high period of this clock pulse.
All other devices on the bus remain idle while the selected device
waits for data to be read from or written to it. If the R/
W
bit is a 0,
the master writes to the slave device. If the R/
W
bit is a 1, the
master reads from the slave device.
Step 2
Data is sent over the serial bus in sequences of nine clock pulses:
eight bits of data followed by an acknowledge bit from the slave
device. Data transitions on the data line must occur during the
low period of the clock signal and remain stable during the high
period because a low-to-high transition when the clock is high
could be interpreted as a stop signal. If the operation is a write
operation, the first data byte after the slave address is a command
byte. This command byte tells the slave device what to expect next.
It may be an instruction telling the slave device to expect a block
write, or it may be a register address that tells the slave where
subsequent data is to be written. Because data can flow in only
one direction, as defined by the R/
W
bit, sending a command
to a slave device during a read operation is not possible. Before
a read operation, it may be necessary to perform a write operation
to tell the slave what sort of read operation to expect and/or the
address from which data is to be read.
Step 3
When all data bytes have been read or written, stop conditions
are established. In write mode, the master pulls the data line high
during the 10th clock pulse to assert a stop condition. In read
mode, the master device releases the SDA line during the low
period before the ninth clock pulse, but the slave device does not
pull it low. This is known as a no acknowledge. The master then
takes the data line low during the low period before the 10th clock
pulse and then high during the 10th clock pulse to assert a stop
condition.
04735-036
19 91
191 9
START BY
MASTER
ACK. BY
SLAVE
ACK. BY
SLAVE
ACK. BY
SLAVE
ACK. BY
SLAVE
FRAME 2
COMMAND CODE
FRAME 1
SLAVE ADDRESS
FRAME N
DATA BYTE
FRAME 3
DATA BYTE
SCL
SDA
R/W
STOP
BY
MASTER
SCL
(CONTINUED)
SDA
(CONTINUED)
D7A0A11001 1 D6 D5 D4 D3 D2 D1 D0
D7 D6 D5 D4 D3 D2 D1
D0
D7 D6 D5 D4 D3 D2 D1 D0
Figure 36. General SMBus Write Timing Diagram