In the ABEL source, instead of using truth-table we can write equations for each of the outputs directly. ABEL will still minimize them for us. We could replace the truth table block with:
EQUATIONS
d28 = ( !m8 & !m4 & m2 & !m1 & !leap);
d29 = ( !m8 & !m4 & m2 & !m1 & leap);
d30 = ( !m8 & m4 & !m2 & !m1 # !m8 & m4 & m2 & !m1
# m8 & !m4 & !m2 & m1 # m8 & !m4 & m2 & m1);
d31 = ( !m8 & !m4 & !m2 & m1 # !m8 & !m4 & m2 & m1
# !m8 & m4 & !m2 & m1 # !m8 & m4 & m2 & m1
# m8 & !m4 & !m2 & !m1 # m8 & !m4 & m2 & !m1
# m8 & m4 & !m2 & !m1);
Equations specify logic functions with an extended form of Boolean algebra. An ending semicolon is required for each equation. Note in the above equations the symbols used for not, and and or. Not is represented by !, and by & and or by #. The equations statement defines the beginning of a group of equations associated with a device. The equations following the equation statement are any valid ABEL-HDL equations as described in the ABEL-HDL language structure. The resulting minimized equations are same as before. ABEL performs the two level minimization for us.