CODEWITHSUNDEEP
vhdl
user1796876
user1796876

Reputation: 21

Unexpected if vhdl

This error has been mindfucking me for long, I don't know what to do. I get the same error in other codes, but this one is a simple one, so maybe it's easier to find out what's the problem.

It's a frequency selector, if the switch (clau) is on, the frequency changes.

library IEEE;
use IEEE.numeric_bit.ALL; 

-- Uncomment the following library declaration if using
-- arithmetic functions with Signed or Unsigned values
--use IEEE.NUMERIC_STD.ALL;

-- Uncomment the following library declaration if instantiating
-- any Xilinx primitives in this code.
--library UNISIM;
--use UNISIM.VComponents.all;

entity selector_frequencia is
Port ( unHz : in bit ;
       centHz : in bit ;
       Clock : out bit;
          clau: in bit);
end selector_frequencia;

architecture Behavioral of selector_frequencia is

begin
if (clau = "0") then Clock <= unHz;
else Clock <= centHz;
end if;

end Behavioral;

And the error I get is this one:

ERROR:HDLParsers:164 - "C:/Documents and Settings/Administrador/Escritorio/practica_digital/practica_digital/selector_frequencia.vhdl" Line 23. parse error, unexpected IF

Thank you.

Upvotes: 2

Views: 2093

Answers (3)

Alex
Alex

Reputation: 7838

I'm not really an expert in VHDL but I believe you should use the if statement inside a process:

architecture Behavioral of selector_frequencia is

begin

fqsel:PROCESS(unHz , centHz , Clock , clau)
BEGIN

  if (clau = '0') then
      Clock <= unHz;
  else
      Clock <= centHz;
  end if;

END PROCESS fqsel;

end Behavioral;

Upvotes: 3

Charles Steinkuehler
Charles Steinkuehler

Reputation: 3365

As Alex pointed out, your if statement needs to be inside a process block. In addition, VHDL is not C...you are not supposed to put parens () around the conditional or it looks like a procedure/function call or a signal range ie: my_bus(7 downto 0) but it's a syntax error because if is a reserved word. Try:

process (clau, unHz, centHz)
begin
  if clau = '0' then 
    Clock <= unHz;
  else 
    Clock <= centHz;
  end if;
end process;

Finally, outside of a process, you can just use a conditional signal assignment, which is a short-hand way of implementing the equivalent process and if statements:

Clock <= unHz when clau='0' else centHz;

Upvotes: 1

Vaibhav Desai
Vaibhav Desai

Reputation: 2728

You are using an assignment statement in your IF clause:

// This is assignment, you are assigning 'clau' to 0 and then checking it in 'if'
if (clau = "0") then Clock <= unHz;

// Try this, note the double '='
if (clau == "0") then Clock <= unHz;

Assignment statements should be within a PROCESS block.

Hope this helps.

Upvotes: 0

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