User's Manual

3-3
ADVANCED MATH FEATURES
3.2.2 Fractional Mode
A signed fractional contains an imaginary decimal point between the sign bit (the MSB) and the
adjacent bit. These examples illustrate the representation of 32-bit signed fractional numbers:
0.111 1111 1111 1111 1111 1111 1111 1111
0.000 0000 0000 0000 0000 0000 0000 0000 = 0
1.111 1111 1111 1111 1111 1111 1111 1111 =
1.000 0000 0000 0000 0000 0000 0000 0000 = –1
Fractional mode shifts the result of a multiplication instruction left by one bit before writing the
result to the accumulator. This left shift eliminates the extra sign bit when both operands are
signed, leaving a correctly signed result and the correct decimal placement.
2147483647
2147483648
---------------------------------
1==
1–
2147483648
---------------------------------
0–=