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Altera_Forum
Honored Contributor I
1,227 Views

Flip-flop by using logic gates

hi 

 

I am a new to VHDL and currently doing VHDL assignment. In this assignment, required to create the D, JK flip-flop.  

 

I need help to solve my error for my code as shown as below:  

 

library ieee; 

use ieee.std_logic_1164.all; 

 

library work; 

 

entity Lab1 is  

 

port 

J :in std_logic; 

K :in std_logic; 

clk :in std_logic; 

Q : out std_logic; 

qn :out std_logic 

); 

 

end Lab1; 

 

architecture arc of Lab1 is 

 

signal W1 : std_logic; 

signal W2 : std_logic; 

signal W3 : std_logic; 

signal W4 : std_logic; 

signal W5 : std_logic; 

signal W6 : std_logic; 

 

begin 

 

qn <= W4; 

W1 <= not (J and clk and W4);  

W2 <= not (K and clk and W3);  

W3 <= W1 nand W4; 

W4 <= W2 nand W3; 

 

process(clk) 

begin 

 

if rising_edge(clk)then  

Q <=(J and (not Q)) or ((not K) and Q); 

 

qn <=not Q ; 

 

end if; 

end process; 

 

end arc; 

------------------------------------------ 

 

Error (10309): VHDL Interface Declaration error in Lab1.vhd(41): interface object "Q" of mode out cannot be read. Change object mode to buffer. 

 

Pls help me to solve the syntax error  

 

Thanks
0 Kudos
5 Replies
Altera_Forum
Honored Contributor I
107 Views

Two options: 

- change Q from out to buffer 

- use an internal signal Qi and copy it to Q outside the edge sensitive condition. 

 

Also the assignment for qn must be placed outside the rising_edge() condition, otherwise it's delayed by one clock.
Altera_Forum
Honored Contributor I
107 Views

Hi FvM  

 

- use an internal signal Qi and copy it to Q outside the edge sensitive condition? 

 

can show me pls?
Altera_Forum
Honored Contributor I
107 Views

process(clk) begin if rising_edge(clk)then Qi <=(J and (not Qi)) or ((not K) and Qi); end if; qn <=not Qi ; Q <= Qi ; end process;

Altera_Forum
Honored Contributor I
107 Views

BTW, shouldn't  

qn <= not Qi; 

Q <= Qi 

 

be outside the process?
Altera_Forum
Honored Contributor I
107 Views

 

--- Quote Start ---  

BTW, shouldn't  

qn <= not Qi; 

Q <= Qi 

 

be outside the process? 

--- Quote End ---  

 

Yes, they must for correct simulation, or Qi needs to be added to the sensitive list.  

 

Thanks!
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