Adam, I think you’re partially right.

In the datasheet of the AD5934 on page 22 it show data the data from this converter is in 2’s complement.

In the program on page 17 of your reference it also written that it is 2’s complement and that 0x7FFF is 32767. So far I agree.

So in a word (16 bits) data <= 0x7FFF is positive and >=0x8000 is negative


The conversion on page 17 is wrong, I think.

0xFFFF = -1 the conversion on page 17 gives us:

0xFFFF & 0x7FFF = 0x7FFF – 0x7FFF = 0 (1’s complement)


It should be: invert data, add 1 for a 2’s complement conversion

0xFFFF ! = 0 + 1 = -1 because it was >= 0x8000 it is negative

0x8000 ! = 0x7FFF + 1 = -32768 because it was >= 0x8000 it is negative

Like your example


Hope this helps to clear things up