Create a 4x4-bit Bcd
counter which able to count 0000,0001,0002...0009,0010,0011,
..,9998, 9999 and start all over again.
Inspiration can be found in Wakerly chapter 8 (read about the 74xx163
could chose between a single Bcd counter which could be combined
(actually 4 counters) in a schematic, alternatively could you
create a "pure" VHDL solution.
NB! Next task will be
watch counter like 00:00:00 to 23:59:59