The fan speed is controlled by four different modes:

• software DCY control;
• software RPM control,
• auto remote temperature fan control;
• maximum fast-speed calculated control.

The Auto Temperature-Fan Control mode consists of auto remote temperature-fan control and maximum fast-speed calculated control. It is an intelligent closed-loop control. In this mode, the fan speed is controlled either by the remote temperature (Auto-Remote Temperature-Fan Control) or by maximum speed calculated for internal and remote temperature. This control mode optimizes fan speed for a given temperature to intelligently manage the system thermals/acoustics. The user writes the proper registers to define the linear feedback control algorithm parameters. After programming, the AMC6821-Q1 runs stand-alone, even without the intervention of the micro-controller. It ensures that if the controller or system locks up, the fan can still be controlled based on temperature measurements, and the fan speed adjusted to correct any changes in system temperature. Software-RPM works as a fan speed regulator to maintain the speed at a programmable target value. It is a closed-loop mode and can run stand-alone as well. The Software-DCY mode is an open-loop mode; the PWM output duty cycle changes to the target value immediately after the user writes the desired duty cycle to the device registers.

Bits FDRC1 and FDRC0 in Configuration Register 1 determine the operation mode.