Datasheet

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FAN CONTROLLER REGISTERS
AMC6821
SBAS386C – MAY 2006 – REVISED JULY 2007
Status Register 2 (Address 0x03, Value After Power-On or Reset = 0x00)
BIT NAME R/W DEFAULT DESCRIPTION
Status of the THERM pin as an input. When this input is pulled low, THERM-IN = 1, and
7 THERM-IN R 0 the fan is driven at full speed. This bit is cleared when reading this register and be
written to '1' if the pin persists "pulled-low".
Local temperature over the local THERM limit flag. L-THERM = 1 when the local
temperature is greater than the value of the Local-THERM-Limit register. Otherwise,
L-THERM = 0. When L-THERM is set to 1, the THERM pin goes low. It also generates a
6 L-THERM R 0 THERM interrupt through the SMBALERT pin, if enabled (THERMOVIE = 1). This bit is
cleared on a read of Status Register 1 . Once cleared, this bit is not reasserted until the
temperature falls 5 ° C below the THERM limit, even if the THERM condition persists.
Refer to the THERM Pin and External Hardware Control section.
Active control temperature below the PSV (passive cooling) temperature flag. This bit is
set to '1' when the active control temperature is equal to or below the PSV temperature.
Otherwise, this bit is cleared ('0'). LPSV = 1 generates a PSV interrupt on SMBALERT, if
5 LPSV R 0
enabled (PSVIE = 1). This bit is cleared when reading this register. If the active control
temperature remains equal to or below the PSV temperature, this bit reasserts on the
next monitoring cycle.
Local temperature over the local critical temperature flag. This bit is set ('1') when the
local temperature is equal to or above the local critical temperature. LTC = 0 if the local
critical temperature is below this value. LTC = 1 asserts the OVR pin low and generates
4 LTC R 0
an LTC interrupt (non-maskable) though the SMBALERT pin. This bit is cleared when
reading this register. If the over-critical limit condition persists, this bit reasserts on the
next monitoring cycle.
Remote temperature over the remote critical temperature flag. This bit is set to '1' when
the remote temperature is equal to or above the remote critical temperature. RTC = 0 if
the remote critical temperature is below this value. RTC = 1 asserts the OVR pin low and
3 RTC R 0
generates an RTC interrupt (non-maskable) though the SMBALERT pin. This bit is
cleared when reading this register. If the over-critical limit condition persists, this bit
reasserts on next monitoring cycle.
2 Reserved R 0 Reserved. Reading returns '0'.
1 Reserved R 0 Reserved. Reading returns '0'.
0 Reserved R 0 Reserved. Reading returns '0'.
DCY (Duty Cycle) Register (Address 0x22, Value After Power-On or Reset = 0x55)
BIT NAME DEFAULT DESCRIPTION
7 (MSB) DCY7 (MSB) 0 DCY CODE DUTY CYCLE
6 DCY6 1 0x00 0%
5 DCY5 0 0x01 0.392%
4 DCY4 1 ... ... ... ...
3 DCY3 0 0x40 25%
2 DCY2 1 ... ... ... ...
1 DCY1 0 0x80 50%
0 DCY0 1 ... ... ... ...
0xFF 100%
The DCY register stores the value of the PWM duty cycle, 0x00 corresponds to 0%, and 0xFF to 100%. 1LSB
corresponds to 0.392%. Power-on default = 0x55, 33.2%.
In a read operation, with the two following exceptions, the returned data are the actual duty cycle (DCY) value
driving the PWM-Out pin:
1. When TACH-MODE = 0 and the system is in software-RPM control mode, if the calculated duty cycle is less
than 30%, the returned value is the calculated value, not the actual PWM-OUT pin duty cycle which is forced
to 30%.
2. When TACH-MODE = 0 and the system is in software DCY-control mode or Auto Temperature-Fan mode, if
the calculated duty cycle is less than 7%, the returned value is the calculated value, not the actual
PWM-OUT pin duty cycle which is forced to 0%.
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