Re: Digital Logic Problem
Well CMOS, I can't really tell the difference between what you called "A: ENABLED", "B: DISABLED", "C: P", "D: DISABLED" and ("C: Q" and "C: R" or "C: S"), but if we name the bits of your 14-bits word as [W13..W0] (W13 MSB), you could test (logical AND with '1') the four least significant 4 bits of your final word (i.e. W3, W2, W1 and W0).
The combination of logical '0's you get would indicate the selected "options".
In your example:
3FF0h --> [W3..W0]=0000, which means:
D disabled (because result > 0Fh);
B enabled (W3=0);
A disabled (W2=0);
C: R (W1=0);
C: Q (W0=0);
or
C: S (W1=0 and W0=0)
or I totally missed your question...