regcnt.vhd

Xilinx Ise 官方源代码盘 第四章

library LIB;
use LIB.SYNOPSYS.all; 
use LIB.AMD_PACK.all; 

entity REGCNT is
  port(OPERATION : in REGCNT_OPS;
       DATA      : in ADDRESS; 
       CLOCK     : in BIT; 
       OUTPUT    : buffer ADDRESS; 
       ZERO      : out BIT); 
end REGCNT; 

architecture REGCNT_HDL of REGCNT is 
begin 

  process 
  begin 
    wait until not CLOCK'stable and CLOCK = '1'; 
 
    if OPERATION = LOAD then 
      OUTPUT <= DATA;
    elsif OPERATION = DEC then 
      OUTPUT <= OUTPUT - 1;
    end if; 

  end process; 

  ZERO <= BIT_OF(OUTPUT = ADDRESS'(others => '0'));
end REGCNT_HDL;