MSP430F248: XT2 range selection of register BCSCTL3 not match with User Manual and driver library, also affect power consumption .

Hello Vincent,

When looking at application notes, user guides, example software, or even header files, it is important to keep in  mind the scope of these documents. Typically, these type of collateral are written for more than one device, and in fact whole families of devices. Also, sometimes the document is based off the first device in the family, and has not been updated to reflect different values in potentially "newer" device sin the family. this is especially true in such a diverse family as the MSP430x2xx family of MSP430 MCUs.  This means, sometimes you will see discrepancies as you pointed out. When this happens, the device specific Datasheet is the highest authority for the device.

for your device, the MSP430F248, you can see in section Crystal Oscillator XT2, the different frequency ranges the different modes cover (XTSx setting). For this particular device, Mode 1 can cover a range of 1-4 MHz, while mode two can cover 2-16 MHz depending on voltage. This means with your XT2 frequency of 3.6864MHz, you could use either mode 1 or 2.

Now, the different modes will correspond with different drive strengths for the Xtal with generally the higher the mode, the greater the drive strength. This increased drive strength translates to more current. So I'm not surprised you see a big current difference between the two modes. For your setup, I would recommend using mode 1. 

Hello Vincent,

As mentioned earlier, it is in the section/table Crystal Oscillator XT2 in the datasheet. Page 51 in the current revision. I've included a snippet below.