4.5 Integer Constants
AVRASM2 allows underscores (_) to be used as separators for increased readability. Underscores may be located anywhere in the number except as the first character or inside the radix specifier.
Example:
0b1100_1010
and 0b_11_00_10_10_
are both legal, while
_0b11001010
and 0_b11001010
are not.