1.7. Non-IEEE-754 Standard Format
The fixed-point data type is similar to the conventional integer data type, except that the fixed-point data carries a predetermined number of fractional bits. If the width of the fraction is 0, the data becomes a normal signed integer.
The notation for fixed-point format numbers in this user guide is Qm.f, where Q designates that the number is in Q format notation, m is the number of bits used to indicate the integer portion of the number, and f is the number of bits used to indicate the fractional portion of the number.
For example, Q4.12 describes a number with 4 integer bits and 12 fractional bits in a 16-bit word.
The following figures show the difference between the signed-integer format and the fixed-point format for a 32-bit number.