ADT7490 Datasheet, PDF (18/75 Pages) Analog Devices – dBCool Remote Thermal Monitor and Fan Controller with PECI Interface

ADT7490
Table 8. PECI Error Indicators
PECI
Data
0x8000 to
0x8003
Invalid
FCS
Description
PECI data error
PECI communications error
Action
Bit 1 of Register
0x43 is set to 1
Bit 2 of Register
0x43 is set to 1
Each PECI channel also has an associated status bit to
indicate if the PECI high or low limits have been exceeded.
An alert is generated on the SMBALERT pin when these
status bits are asserted.
Table 9. PECI Status Bits
Channel
PECI0
PECI1
PECI2
PECI3
Register
Bit
0x43
0
0x81
3
0x81
4
0x81
5
Temperature Data REPLACE Mode
The REPLACE mode is configured by setting Bit 4 of
Register 0x36. In this mode, the data in the existing Remote
1 registers are replaced by PECI0 data. This is a legacy mode
that allows the thermal data from CPU1 to be stored in the
same registers as in the ADT7476A. This reduces the
software changes in systems transitioning from CPUs with
thermal diodes to CPUs with a PECI interface. However,
note that even though the associated registers are swapped,
the correct data format (PECI vs. absolute temperature, see
Table 2) must be written to and interpreted from these
registers.
Notes
In Table 10, registers listed under the Remote 1 Default
column are in absolute temperature format by default and
are in PECI format in REPLACE mode. Registers listed
under the PECI0 Default column are in PECI format by
default and in absolute temperature format in REPLACE
mode.
Table 10. Replace Mode Temperature Registers
Register Name
Remote 1
Default
PECI0 Default
Value Register
Reg. 0x25
Reg. 0x33
Low Limit
Reg. 0x4E
Reg. 0x34
High Limit
Reg. 0x4F
Reg. 0x35
T_MIN
T_RANGE
Reg. 0x67
Reg. 0x5F,
Bits [7:4]
Reg. 0x3B
Reg. 0x3C,
Bits [7:4]
Enhanced Acoustics
Reg. 0x62,
Bits [2:0]
Reg. 0x3C,
Bits [2:0]
Enhanced Acoustics
Enable
Reg. 0x62, Bit 3 Reg. 0x3C, Bit 3
THERM T_CONTROL
T_MIN Hysteresis
Reg. 0x6A
Reg. 0x6D,
Bits [7:4]
Reg. 0x6D,
Bits [3:0]
(Note 1)
Reg. 0x3D
Reg. 0x6E,
Bits [3:0]
Reg. 0x6E,
Bits [7:4]
(Note 1)
Temperature offset
Reg. 0x70
Reg. 0x94
Operating Point for
Dynamic T_MIN
Reg. 0x8B
Reg. 0x8A
1. In REPLACE mode, the Remote 2 and local temperature hys-
teresis values are swapped.
In REPLACE mode, the temperature zone controlling the
relevant PWM output are also swapped from Remote 1 to
PECI0. The swap of control only occurs if the default
behavior setting for Register 0x5C Bits [7:5], Register 0x5D
Bits [7:5] or Register 0x5E Bits [7:5] is 000.
Local Temperature Measurement
The ADT7490 contains an on−chip band gap temperature
sensor whose output is digitized by the on−chip 10−bit ADC.
The 8−bit MSB temperature data is stored in the local
temperature register (Address 0x26). Because both positive
and negative temperatures can be measured, the temperature
data is stored in Offset 64 format or twos complement
format, as shown in Table 11 and Table 12. Theoretically, the
temperature sensor and ADC can measure temperatures
from −128°C to +127°C (or −64°C to +191°C in the
extended temperature range) with a resolution of 0.25°C.
However, this exceeds the operating temperature range of
the device, so local temperature measurements outside the
ADT7490 operating temperature range are not possible.
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