Datasheet

Data Sheet ADT7420
Rev. 0 | Page 13 of 24
REGISTERS
The ADT7420 contains 14 registers:
• Nine temperature registers
• A status register
• An ID register
• A configuration register
• An address pointer register
• A software reset
All registers are eight bits wide. The temperature value registers,
the status register, and the ID register are read-only. The software
reset is a write-only register. On power-up, the address pointer
register is loaded with 0x00 and points to the temperature value
most significant byte register (Register Address 0x00).
Table 6. ADT7420 Registers
Register
Address Description
Power-On
Default
0x00 Temperature value most significant byte 0x00
0x01 Temperature value least significant byte 0x00
0x02 Status 0x00
0x03 Configuration 0x00
0x04
T
HIGH
setpoint most significant byte
0x20 (64°C)
0x05 T
HIGH
setpoint least significant byte 0x00 (64°C)
0x06 T
LOW
setpoint most significant byte 0x05 (10°C)
0x07 T
LOW
setpoint least significant byte 0x00 (10°C)
0x08 T
CRIT
setpoint most significant byte 0x49 (147°C)
0x09 T
CRIT
setpoint least significant byte 0x80 (147°C)
0x0A T
HYST
setpoint 0x05 (5°C)
0x0B ID 0xCB
0x2F Software reset 0xXX
ADDRESS POINTER REGISTER
This register is always the first register written to during a write
to the ADT7420. It should be set to the address of the register
to which the write or read transaction is intended. Table 7
shows the register address of each register on the ADT7420.
The default value of the address pointer register is 0x00.
Table 7. Address Pointer Register
P7 P6 P5 P4 P3 P2 P1 P0
ADD7 ADD6 ADD5 ADD4 ADD3 ADD2 ADD1 ADD0
TEMPERATURE VALUE REGISTERS
The temperature value consists of two bytes, one most signifi-
cant byte and one least significant byte. These values can be
read in two separate 1-byte reads or in a single 2-byte read. For a
2-byte read, only the address of the most significant byte must be
loaded into the address pointer register. After the most signifi-
cant byte is read, the address pointer is auto-incremented so that
the least significant byte can read within the same transaction.
Bit 0 to Bit 2 are event alarm flags for T
LOW
, T
HIGH
, and T
CRIT
. When
the ADC is configured to convert the temperature to a 16-bit
digital value, then Bit 0 to Bit 2 are no longer used as flag bits
and are instead used as the LSBs for the extended digital value.
Table 8. Temperature Value MSB Register (Register Address 0x00)
Bit Default Value Type Name Description
[14:8] 0000000 R Temp Temperature value in twos complement format
15 0 R Sign Sign bit, indicates if the temperature value is negative or positive
Table 9. Temperature Value LSB Register (Register Address 0x01)
Bit
Default
Value Type Name Description
0 0 R T
LOW
flag/LSB0 Flags a T
LOW
event if the configuration register, Register Address 0x03[7] = 0 (13-bit
resolution). When the temperature value is below T
LOW
, this bit it set to 1.
Contains the Least Significant Bit 0 of the 15-bit temperature value if the configuration
register, Register Address 0x03[7] = 1 (16-bit resolution).
1
0
R
T
HIGH
flag/LSB1
Flags a T
HIGH
event if the configuration register, Register Address 0x03[7] = 0 (13-bit
resolution). When the temperature value is above T
HIGH
, this bit it set to 1.
Contains the Least Significant Bit 1 of the 15-bit temperature value if the configuration
register, Register Address 0x03[7] = 1 (16-bit resolution).
2 0 R T
CRIT
flag/LSB2 Flags a T
CRIT
event if the configuration register, Register Address 0x03[7] = 0 (13-bit
resolution). When the temperature value exceeds T
CRIT
, this bit it set to 1.
Contains the Least Significant Bit 2 of the 15-bit temperature value if the configuration
register, Register Address 0x03[7] = 1 (16-bit resolution).
[7:3] 00000 R Temp Temperature value in twos complement format.