Howdy Eli,
The AMC6821 EVM is currently only compatible with Windows XP Operating systems. The EVM uses an older interface board, the USBMODE EVM, which only operates with the earlier Windows XP driver. There is no current plan to upgrade the software for this EVM, but if the demand for this product is great we can definitely relay the urgency for updated EVM software.
To answer your questions:
1. The TACH limits are specified in the TACH Limit register. The larger value of the TACH data corresponds to a slower speed. When the TACH data are larger than the TACH-Low-Limit, the fan runs at a speed below the predefined minimum RPM. When the TACH data are less than the TACH-High-Limit, the fan runs at a speed above the predefined maximum RPM. (page 19 of DS). These limits can be set in Reg 0x10, 0x11.
2. In Software-RPM Mode, The user writes the proper value in the TACH Setting Register to set the target fan speed. The actual fan speed is monitored by an on-chip fan speed counter, and the results is stored in the TACH-DATA Register. The actual speed is compared with the setting value. If there is a difference, the duty cycle is adjusted. You can reset the RPM value by writing to the TACH Setting Register.
3. This can be set in the TACH Setting Register.
4. The AMC6821 has two address bits, making it capable to share a maximum of 4 devices on one I2C Bus. To include more devices, you may need more I2C lines, or a mux controller for the address lines.
Hope this information helps,
Matt