ADT7476
Rev. B | Page 23 of 72
Changing Bit 1 of Configuration Register 5 (0x7C) changes the
resolution and therefore the range of the temperature offset as
either having a range of –63°C to +127°C with a resolution of
1°C or having a range of −63°C to +64°C with a resolution of
0.5°C. This temperature offset can be used to compensate for
linear temperature errors introduced by noise.
Temperature Offset Registers
Register 0x70, Remote 1 Temperature Offset = 0x00 (0°C default)
Register 0x71, Local Temperature Offset = 0x00 (0°C default)
Register 0x72, Remote 2 Temperature Offset = 0x00 (0°C default)
ADT7463/ADT7476 Backwards Compatible Mode
By setting Bit 0 of Configuration Register 5 (0x7C), all tempera-
ture measurements are stored in the zone temperature value
registers (Register 0x25, Register 0x26, and Register 0x27) in
twos complement in the range −63°C to +127°C. The tempera-
ture limits must be reprogrammed in twos complement.
If a twos complement temperature below −63°C is entered, the
temperature is clamped to −63°C. In this mode, the diode fault
condition remains −128°C = 1000 0000, while in the extended
temperature range (−63°C to +191°C), the fault condition is
represented by −64°C = 0000 0000.
Temperature Measurement Registers
Register 0x25, Remote 1 Temperature
Register 0x26, Local Temperature
Register 0x27, Remote 2 Temperature
Register 0x77, Extended Resolution 2 = 0x00 default
Bits [7:6] TDM2, Remote 2 temperature LSBs
Bits [5:4] LTMP, Local temperature LSBs
Bits [3:2] TDM1, Remote 1 temperature LSBs
Temperature Measurement Limit Registers
Associated with each temperature measurement channel are high
and low limit registers. Exceeding the programmed high or low
limit causes the appropriate status bit to be set. Exceeding either
limit can also generate SMBALERT interrupts (depending on the
way the interrupt mask register is programmed and assuming
that SMBALERT is set as an output on the appropriate pin).
Register 0x4E, Remote 1 Temperature Low Limit = 0x81 default
Register 0x4F, Remote 1 Temperature High Limit = 0x7F default
Register 0x50, Local Temperature Low Limit = 0x81 default
Register 0x51, Local Temperature High Limit = 0x7F default
Register 0x52, Remote 2 Temperature Low Limit = 0x81 default
Register 0x53, Remote 2 Temperature High Limit = 0x7F default
Reading Temperature from the ADT7476
It is important to note that temperature can be read from the
ADT7476 as an 8-bit value (with 1°C resolution) or as a 10-bit
value (with 0.25°C resolution). If only 1°C resolution is required,
the temperature readings can be read back at any time and in no
particular order.
If the 10-bit measurement is required, this involves a 2-register
read for each measurement. The extended resolution register
(0x77) should be read first. This causes all temperature reading
registers to be frozen until all temperature reading registers
have been read from. This prevents an MSB reading from being
updated while its two LSBs are being read and vice versa.
ADDITIONAL ADC FUNCTIONS FOR
TEMPERATURE MEASUREMENT
Several other functions are available on the ADT7476 to offer
the system designer increased flexibility.
Turn-Off Averaging
For each temperature measurement read from a value register,
16 readings are actually made internally, and the results averaged,
before being placed into the value register. Sometimes it is
necessary to take a very fast measurement. Setting Bit 4 of
Configuration Register 2 (0x73) turns averaging off. The default
round-robin cycle time is 146.5 ms.
Table 12. Conversion Time with Averaging Disabled
Channel Measurement
Time
(ms)
Voltage Channels
0.7
Remote Temperature 1
7
Remote Temperature 2
7
Local Temperature
1.3
When Bit 7 of Configuration Register 6 (0x10) is set, the default
round-robin cycle time increases to 240 ms.
Table 13. Conversion Time with Averaging Enabled
Channel Measurement
Time
(ms)
Voltage Channels
11
Remote Temperature
39
Local Temperature
12
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