Excess-3 to binary decoder using unused combinations of the code as don't-care condition

This problem is from my textbook chapter review question, and it seems a lot different from the example provided by textbook, so I have no idea what to do.

I even have solution manual for this, but still, I'm totally lost.

I drew the table as following: I set don't care condition as d(0,1,2,13,14,15).

Textbook solution is: w(A,B,C,D)=m(11,12) x(A,B,C,D)=m(7,8,9,10) y(A,B,C,D)=m(5,6,9,10) z(A,B,C,D)=m(4,6,8,10,12)

Please help me how to get those min-terms based on what method. Some min-terms are selected when both excess-3 and binary both have the value of 0. (especially on 'w')

Only one thing I can figure out is how to get the min-terms for 'z' which is z(A,B,C,D)=m(4,6,8,10,12) where I can just place 1 in k-map followed by the value of the last digit on excess-3 table

• Only one thing I understand is how to get the 'z' which is z(A,B,C,D)=m(4,6,8,10,12) where I can just place 1 in k-map followed by the value of the last digit on excess-3 table. – Minjae Jul 11 '16 at 21:41
• A Don't Care condition can be true or false as needed. Do your K-Maps and update your question with what you find. Sometimes it is just a matter of ignoring a solution and doing it yourself. – StainlessSteelRat Jul 12 '16 at 0:44
• Use karnaughs mapping.For each w,x,y and z. – Zulfiqar Ali Nov 22 '18 at 19:38