NCT7491
http://onsemi.com
22
" If bit 5 of 0x11 is 1 then PWM1 will go to 100% duty
or Max duty. If bit 5 is 0 then the error is ignored.
" If bit 6 of 0x11 is 1 then PWM2 will go to 100% duty
or Max duty. If bit 6 is 0 then the error is ignored.
" If bit 7 of 0x11 is 1 then PWM3 will go to 100% duty
or Max duty. If bit 7 is 0 then the error is ignored.
Whether the PWM outputs go to 100% or Max duty is
determined by bits <4:2> of register 0x16. See the THERM
ASSERTION section of this document for more details.
SMBus Master Status Registers
" Bad Block read byte count, 0x81 bit 6
" NACK bits, 0xB6 bits <7:0>
" PEC error bits, 0xB7 bits <7:0>
" SMBus Timeout bits, 0xB8 bits <7:0>
" High/Low Limit exceeded bits, 0xB9 bits <7:0>
" PCH Data Invalid, 0xBA bits <4:0>
" THERM Limit exceeded, 0xBB bits <7:0>
Bad Block Read Count will assert if the byte count returned
by the block read command is insufficient to read the
required temperatures.
NACK bits will assert if a device does not acknowledge its
SMBus address.
PEC error bits will assert if the PEC byte is incorrect.
SMBus Timeout bits will assert if the bus is locked.
High/Low Limit bits will assert if the temperature returned
is at or below the programmed low limit value.
PCH Data Invalid bits will assert if the PCH returns
reserved temperature codes
THERM Limit bits will assert if the returned temperature
is greater than the programmed THERM limit
The status bits ((except THERM status) will hold their
value until the registers are read through the SMBus slave
port. Status bits (except THERM status) can be masked by
setting the corresponding bits in registers 0xBB to 0xBF.
THERM Limit status bits will automatically clear when the
temperature is below the SMBus THERM limit, unless
THERM hysteresis is enabled (setting bit 0 of register 0x11)
in which case the temperature must drop below THERM
limit Hysteresis.
Automatic Fan Control
There are two automatic fan control methods that can be
selected in the NCT7491. Each PWM channel can be set to
use the Tmin/Trange control method or to use an 8 point
PWM LookUp Table. In both cases one or more
temperature channels can be assigned to control each PWM
output.
Assigning Temperature Zones for Automatic Fan Control
These registers allow the temperature zone to be assigned
to a PWM channel by setting the appropriate bit. Any
combination of temperature zones can be assigned to control
any fan. If more than one zone is selected then a PWM value
will be calculated for each temperature and the highest
calculated PWM value will be output. If no temperature
sources are selected then the associated PWM channel
defaults to manual mode.
Registers for assigning zones to PWM1:
" Local/Remote1/Remote2 Control, 0x8A bits <2:0>
" PECI Control, 0x8A, bits <6:3>
" SMBus Thermal Slave Control, 0x8B bits <7:0>
" Push Temperature Control, 0x8C bits <3:0>
Registers for assigning zones to PWM2:
" Local/Remote1/Remote2 Control, 0x8D bits <2:0>
" PECI Control, 0x8D, bits <6:3>
" SMBus Thermal Slave Control, 0x8E bits <7:0>
" Push Temperature Control, 0x8F bits <3:0>
Registers for assigning zones to PWM3:
" Local/Remote1/Remote2 Control, 0x90 bits <2:0>
" PECI Control, 0x90, bits <6:3>
" SMBus Thermal Slave Control, 0x91 bits <7:0>
" Push Temperature Control, 0x92 bits <3:0>
For example if the user wants to control PWM1 from the
hottest of the CPU temperature, PCH temperature and the
Remote1 sensor then the Control Source registers would be
programmed as:
" 0x8A <3> = 1 (PECI0)
" 0x8A <1> = 1 (Remote1)
" 0x8B <0> = 1 (SMBus Device 0, PCH)
Tmin/Trange Automatic Fan Control
The PWM channels can be put into Tmin/Trange in the
following way:
" Setting bit <0> of register 0x10 to 0 puts PWM1 in
Tmin/Trange mode
" Setting bit <1> of register 0x10 to 0 puts PWM2 in
Tmin/Trange mode
" Setting bit <2> of register 0x10 to 0 puts PWM3 in
Tmin/Trange mode
PWMmax
Tmin
Fan Off or
PWMmin
100%
Trange
THERM
PWMmin
Figure 11. PWM Control Curve in Tmin/Trange Mode
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