将两个8位寄存器读入C中的ADXL362的12位值

Question

I'm querying an ADXL362 Digital Output MEMS Accelerometer for its axis data which it holds as two 8 bit registers which combine to give a 12 bit value and I'm trying to figure out how to combine those values. I've never been good at bitwise manipulation so any help would be greatly appreciated. I would imagine it is something like this:

number = Z_data_H << 8 | Z_data_L;
number  = (number & ~(1<<13)) | (0<<13);
number  = (number & ~(1<<14)) | (0<<14);
number  = (number & ~(1<<15)) | (0<<15);
number  = (number & ~(1<<16)) | (0<<16);

ADXL362 data sheet (page 26)

Z axis data register

Answer 1

You just have to do:

signed short number;

number = Z_data_H << 8 | Z_data_L;

The shift left by 8 bit combined with the lower bits you already had figured out are combining the 2 bytes correctly. Just use the appropriate data size to have the C code recoginize the sign of the 12 bit number correctly.

Note that short not necessarily refers to a 16bit value, depending on your compiler and architecture - so, you might want to attempt to that.

Answer 2

Your first line should be what you need:

int16_t number;
number = (Z_data_H << 8) | Z_data_L;

The sign-extension bits mean that you can read the value as if it was a 16-bit signed integer. The value will simply never be outside the range of a 12-bit integer. It's important that you leave those bits intact in order to handle negative values correctly.