ADT7408CCPZ-R2 AD [Analog Devices], ADT7408CCPZ-R2 Datasheet - Page 17

• Manufacturer Part Number: ADT7408CCPZ-R2
• Description: +-2 C Accurate, 12-Bit Digital Temperature Sensor
• Manufacturer: AD [Analog Devices]

SERIAL INTERFACE
Control of the ADT7408 is carried out via the SMBus-/I
compatible serial interface. The ADT7408 is connected to this
bus as a slave and is under the control of a master device.
Figure 13 shows a typical SMBus/I
Serial Bus Address
Like all SMBus-/I
serial address. The four MSBs of this address for the ADT7408 are
set to 0011. The three LSBs are set by Pin 1, Pin 2, and Pin 3
(A0, A1, and A2). These pins can be configured either low or
high, permanently or dynamically, to give eight different
address options. Table 11 shows the different bus address
options available. Recommended pull-up resistor value on the
SDA and SCL lines is 2.2 kΩ to 10 kΩ .
Table 11. SMBus/I
BINARY
A6 to A0
0011 0 0 0
0011 0 0 1
0011 0 1 0
0011 0 1 1
0011 1 0 0
0011 1 0 1
0011 1 1 0
0011 1 1 1
The ADT7408 has been designed with a SMBus/I
The SMBus/I
activity on the SDA line. After this timeout the ADT7408 resets
the SDA line back to its idle state (SDA set to high impedance)
and waits for the next start condition.
10kΩ
PULLUP
V
DD
Figure 13. Typical SMBus/I
2
C interface times out after 75 ms to 100 ms of no
EVENT#
A0
A1
A2
2
C-compatible devices, the ADT7408 has a 7-bit
ADT7408
2
C Bus Address Options
GND
SDA
SCL
2
C Interface Connection
2
C interface connection.
V
DD
10kΩ
HEX
0x18
0x19
0x1A
0x1B
0x1C
0x1D
0x1E
0x1F
PULLUP
V
DD
10kΩ
2
C timeout.
2
C-
Rev. 0 | Page 17 of 24
The serial bus protocol operates as follows:
1.
2.
3.
4.
Any number of bytes of data can be transferred over the serial
bus in one operation. However, 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.
The I
by the device until after this address has been sent twice. On the
eighth SCL cycle of the second valid communication, the serial
bus address is latched in. This is the SCL cycle directly after the
device has seen its own I
changes on this pin have no effect on the I
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 an address/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 address (MSB first) plus a R/ W bit.
The R/ W bit determines whether data is written to, or read
from, the slave device.
The peripheral with the address corresponding 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. All other devices on the bus now
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, then the
master writes to the slave device. If the R/ W bit is a 1, the
master reads from the slave device.
Data is sent over the serial bus in sequences of nine clock
pulses: eight bits of data followed by an acknowledge bit
from the receiver of 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 can be interpreted as a
stop signal.
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 pulls the
data line high during the low period before the ninth clock
pulse. This is known as no acknowledge. The master then
takes the data line low during the low period before the
10th clock pulse, then high during the 10th clock pulse to
assert a stop condition.
2
C address set up by the three address pins is not latched
2
C serial bus address. Any subsequent
2
C serial bus address.
ADT7408