Design Challenge - Addition Free Digital Clock

[hamster]

If you want a bit of an FPGA challenge here is one for you.

 

Everybody knows that addition is the most basic math function, and you can't do anything useful without it .

 

Design and implement a Digital clock, but without using any addition  

 

The design has pretty simple specs:

* Output is a 12 hour display (time shown as 1:00 through 12:59), on the seven segment display

* Inputs are two push buttons, one to set the hour and the other to set the minute

* On power-on the time resets to 12:00

* No addition to be used anywhere in the design - and implementing your own adders using boolean logic is cheating!

* Time keeping has accuracy matching that of the system clock

* You can't use any IP cores in the design