Hi friends!, well, I have VHDL code attach (so simply), and I'd like add 
two operations more, CALL and RETURN, so I need Stack Pointer (SP) 
[register], it must be point at the end of the memory and stack should 
start at high addresses and as it grows move to lower addresses, the SP 
in memory will be store programcounter where jump when return. I use 
this simple memory file (also attach).
How I can do it?, I dont know how save programcounter in memory pointed 
by sp.

Thanks in advance, and sorry, i'm newbie.