Need Help in Parallel to Serial VHDL module

parallel to serial vhdl

Hello
I have a question about the following VHDL code to convert from parallel to serial:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

entity PAR2SER is
Port ( DIN : in STD_LOGIC;
MODE : in STD_LOGIC;
CLK : in STD_LOGIC;
RESET : in STD_LOGIC;
SDOUT : out STD_LOGIC);
end PAR2SER;

-- purpose: Implement main architecture of PAR2SER

architecture BEHAVIOR of PAR2SER is

signal IDATA : std_logic_vector(7 downto 0); -- internal data

begin -- BEHAVIOR

-- purpose: Main process

process (CLK, RESET)
begin -- process
-- activities triggered by asynchronous reset (active high)
if RESET = ’1’ then
SDOUT <= ’0’;
IDATA <= "00000000";

-- activities triggered by rising edge of clock

elsif CLK’event and CLK = ’1’ then
case MODE is
when "00" => -- no operation
null;
when "01" => -- load operation
IDATA <= DIN;
when "10" => -- shift left
SDOUT <= IDATA(7);
for mloop in 6 downto 0 loop
IDATA(mloop+1) <= IDATA(mloop);
end loop; -- mloop
when others => -- no operation otherwise
null;
end case;
end if;
end process;
end BEHAVIOR;

I may sound silly but what's the mode pin for ??

parallel to serial shift register vhdl

The author apparently regarded it useful to control serializer operation with a mode input. There are other options, too. You have to know your requirements.

But the code has a syntactical error, cause mode input is a single std_logic bit but used as a vector. It can't compile as is.

parallel to serial vhdl code

True what FvM says.
Moreover I've to tell you that this is a very bad way of code VHDL.
The construct FOR shall never being used: that's not "C".

You can do in a lot of different manner, the better I think is instantiate a counter and use a shift register.
In VHDL you've to figure out what are you realizing with the Flip Flop.

serial to parallel vhdl

The for loop in this place is OK, it's just another (long winded) way to write a shift register. This is the same function in a single line: