ADT7420 Analog Devices, ADT7420 Datasheet - Page 17

• Manufacturer Part Number: ADT7420
• Description: 16-Bit Digital I2C Temperature Sensor
• Manufacturer: Analog Devices

Preliminary Technical Data
SERIAL INTERFACE
Control of the ADT7420 is carried out via the I
serial interface. The ADT7420 is connected to this bus as a slave
and is under the control of a master device.
Figure 13 shows a typical I
SERIAL BUS ADDRESS
Like all I
address. The five MSBs of this address for the ADT7420 are set
to 10010. Pin A1 and Pin A0 set the two LSBs. These pins can
be configured two ways, low and high, to give four different
address options. Table 20 shows the different bus address options
available. The recommended pull-up resistor value on the SDA
and SCL lines is 10 kΩ.
Table 20. I
A6
1
1
1
1
The serial bus protocol operates as follows:
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 an address/data stream is going
to follow. 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 read/
write (R/ W ) bit. The R/
written to, or read from, the slave device.
A5
0
0
0
0
2
C-compatible devices, the ADT7420 has a 7-bit serial
2
C Bus Address Options
A4
0
0
0
0
Binary
A3
1
1
1
1
2
C interface connection.
W bit determines whether data is
A2
0
0
0
0
ON MICROCONTROLLER
TO INTERRUPT PIN
A1
0
0
1
1
10kΩ
PULL-UP
V
DD
2
C-compatible
A0
0
1
0
1
Figure 13. Typical I
10kΩ
PULL-UP
Hex
0x48
0x49
0x4A
0x4B
V
DD
Rev. PrA | Page 17 of
CT
INT
A0
A1
ADT7420
2
C Interface Connection
GND
SDA
SCL
V
DD
2.
3.
4.
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.
V
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 then
remain idle while the selected device waits for data to be
read from or written to it. If the R/
writes to the slave device. If the R/
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 as a low-to-high transition when
the clock is high, which can be interpreted as a stop signal.
When all data bytes have been read or written, stop condi-
tions are established. In write mode, the master pulls the
data line high during the 10
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 a no acknowledge. The master
takes the data line low during the low period before the
10
assert a stop condition.
DD
th
0.1µF
10kΩ
clock pulse, then high during the 10
PULL-UP
V
DD
10kΩ
th
clock pulse to assert a stop
W bit is a 1, the master
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W bit is a 0, the master
th
clock pulse to
ADT7420