-- Copyright © 1993 by  McGraw-Hill, Inc. and Zainalabedin Navabi

-- FIGURE 9.44 




-- ENTITY DECLARATION OF PARWAN PROGRAM COUNTER UNIT :

LIBRARY cmos;
USE cmos.basic_utilities.ALL;
LIBRARY par_library;
USE par_library.par_utilities.ALL;
--
ENTITY program_counter_unit IS
  PORT (i12 : IN twelve; o12 : OUT twelve; 
        increment, load_page, load_offset, reset, ck : IN qit);
END program_counter_unit;
--


-- BEHAVIORAL DESCRIPTION OF PARWAN PROGRAM COUNTER UNIT :

ARCHITECTURE behavioral OF program_counter_unit IS
BEGIN
  PROCESS (ck)
    VARIABLE internal_state : twelve := zero_12;
  BEGIN
    IF (ck = '0' ) THEN
      IF reset = '1' THEN 
        internal_state := zero_12;
      ELSIF increment = '1' THEN 
        internal_state := inc (internal_state);
      ELSE
        IF load_page = '1' THEN 
          internal_state (11 DOWNTO 8) := i12 (11 DOWNTO 8);
        END IF;
        IF load_offset = '1' THEN 
          internal_state (7 DOWNTO 0) := i12 (7 DOWNTO 0);
        END IF;
      END IF;
      o12 <= internal_state;
    END IF;
  END PROCESS;
END behavioral;
--