PC block contains the logic to generate the value of the program
counter. It also has some interrupt logic and instruction register with
the associated logic. PC talks with the instruction memory through
Iaddrbus and Instrbus. The new value of PC is chosen between Destbus,
Destbus_a, Destbus_b, Aregbus and some increment of the earlier value of
PC. The value of PC is passed through 3 registers where each register
corrsponds to DECODE, EXE and MEM stages respectively. The PC value in the
MEM stage is fed to the IAR.