Datasheet
Data Sheet ADT7420
Rev. 0 | Page 19 of 24
READING DATA
Reading data from the ADT7420 is done in a single data byte
operation for the configuration register, the status register,
the T
HYST
setpoint register, and the ID register. A two data byte
read operation is needed for the temperature value register,
T
HIGH
setpoint register, T
LOW
setpoint register, and the T
CRIT
setpoint register. Reading back the contents of an 8-bit register
similar to the configuration register is shown in Figure 16.
Reading back the contents of the temperature value register
is shown in Figure 17.
Reading back from any register first requires a single-byte write
operation to the address pointer register to set up the address of
the register that is going to be read from. In the case of reading
back from the 2-byte registers, the address pointer automatically
increments from the MSB register address to the LSB register
address.
To read from another register, execute another write to the
address pointer register to set up the relevant register address.
Thus, block reads are not possible, that is, there is no I
2
C address
pointer auto-increment except when reading back from a 16-bit
register. If the address pointer register has previously been set
up with the address of the register that is going to receive a read
command, there is no need to repeat a write operation to set up
the register address again.
SCL
SDA
1
10 01 A10A0
REPEAT START
BY MASTER
FRAME 3
SERIAL BUS ADDRESS
BYTE
FRAME 4
DATA BYTE FROM CONFIGURATION
REGISTER
STOP BY
MASTER
ACK. BY
ADT7420
NO ACK. BY
MASTER
R/W D7D6 D5D4D3D2 D1D0
991
SCL
SDA
1
10 01 A1A0
START BY
MASTER
FRAME 1
SERIAL BUS ADDRESS
BYTE
FRAME 2
ADDRESS POINTER REGISTER BYTE
ACK. BY
ADT7420
ACK. BY
ADT7420
R/W P7P6 P5P4P3P2 P1P0
991
0
09013-018
Figure 16. Reading Back Data from the Configuration Register
NOTES
1. A START CONDITION AT THE BEGINNING IS DEFINED AS A HIGH-TO-LOW TRANSITION ON SDA WHILE SCL REMAINS HIGH.
2. A STOP CONDITION AT THE END IS DEFINED AS A LOW-TO-HIGH TRANSITION ON SDA WHILE SCL REMAINS HIGH.
3. THE MASTER GENERATES THE NO ACKNOWLEDGE AT THE END OF THE READBACK TO SIGNAL THAT IT DOES NOT WANT ADDITIONAL DATA.
4. TEMPERATURE VALUE REGISTER MSB DATA AND TEMPERATURE VALIUE REGISTER LSB DATA ARE ALWAYS SEPARATED BY A LOW ACK BIT.
5. THE R/W BIT IS SET TO A1 TO INDICATE A READBACK OPERATION.
SDA
100
R/W
A7 A6
SCL
SDA
SCL
1
A1 A0
11
0A1A0
9
ADT7410 DEVICE ADDRESS REGISTER ADDRESS[A7:A0]
D1 D0
D7
D6
TEMPERATURE
VALUE REGISTER
MSB DATA
9
1 19 9
01A1A0
R/W
REPEAT
START
D1 D0
D7
D6
ACK. BY
ADT7420
ACK. BY
MASTER
NO
ACK. BY
MASTER
ACK. BY
ADT7420
START
ADT7410 DEVICE ADDRESS
ACK. BY
ADT7420
TEMPERATURE
VALUE REGISTER
LSB DATA
SR
09013-023
Figure 17. Reading Back Data from the Temperature Value Register