通用寄存器.vhd

含有各类寄存器

--Universal Register
--Description - This design is a universal register which can be used as a straightforward storage register, a bi-directional shift register, an up counter and a down counter. The register can be loaded from a set of parallel data inputs
--and the mode is controlled by a 3-bit input. The 'termcnt' (terminal count) output goes high when the register contains zero.
LIBRARY ieee;
USE ieee.Std_logic_1164.ALL;
USE ieee.Std_logic_unsigned.ALL;
ENTITY unicntr IS
GENERIC(n : Positive := 8); --size of counter/shifter
PORT(clock, serinl, serinr : IN Std_logic; --serial inputs
mode : IN Std_logic_vector(2 DOWNTO 0); --mode control
datain : IN Std_logic_vector((n-1) DOWNTO 0); --parallel inputs
dataout : OUT Std_logic_vector((n-1) DOWNTO 0); --parallel outputs
termcnt : OUT Std_logic); --terminal count output
END unicntr;
ARCHITECTURE v1 OF unicntr IS
SIGNAL int_reg : Std_logic_vector((n-1) DOWNTO 0);
BEGIN
main_proc : PROCESS
BEGIN
WAIT UNTIL rising_edge(clock);
CASE mode IS
--reset
WHEN "000" => int_reg <= (OTHERS => '0');
--parallel load
WHEN "001" => int_reg <= datain;
--count up
WHEN "010" => int_reg <= int_reg + 1;
--count down
WHEN "011" => int_reg <= int_reg - 1;
--shift left
WHEN "100" => int_reg <= int_reg((n-2) DOWNTO 0) & serinl;
--shift right
WHEN "101" => int_reg <= serinr & int_reg((n-1) DOWNTO 1);
--do nothing
WHEN OTHERS => NULL;
END CASE;
END PROCESS;
det_zero : PROCESS(int_reg) --detects when count is 0
BEGIN
termcnt <= '1';
FOR i IN int_reg'Range LOOP
IF int_reg(i) = '1' THEN
termcnt <= '0';
EXIT;
END IF;
END LOOP;
END PROCESS;
--connect internal register to dataout port
dataout <= int_reg;
END v1;