Design a Calculator with HCS12

Hello, I need your help with a project: It's designing a calculator via HCS12 assembly programming , using Asmide program to assemble the code and Dragon Board to run it. Design a calculator that can do add, sub, mul, and div with two 4-digit (0 - 9999) decimal numbers. The result of an arithmetic operation will be also a 4-digit decimal number. The HCS12 4x4 keypad will assign to the following characters: 0-9, add(+), sub(-), mul(*),div(/), BS (back-space) and =. The LCD display will display all the numbers and symbols entered using the keypad, and also it will display the result correctly in the given accuracy ( up to 4-digit). Please let me know if you can help me with it. thanks