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Altera_Forum's avatar
Altera_Forum
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12 years ago

Induced delay

I have just started learning how to use VHDL and Quartus and I use it for a Cyclone II FPGA.

I need to write a code , which makes my Output High after a fixed time interval , 60 seconds for example.

Thus I wrote the following code for the same, however it gives me a warning that my Output pins are stuck at VCC and therefore the the Output ( an LED ) , which is ideally supposed to be OFF and glow only after 60 seconds, is always ON.

I also tried using a wait for 60 seconds statement, however that gives me a Wait statement error, saying that at WAIT UNTIL is required.

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

The code is

library IEEE;

use IEEE.STD_LOGIC_1164.ALL;

use IEEE.numeric_std.all;

entity timer is

port ( q : buffer bit := '0');

end entity;

architecture behaviour of timer is

begin

q <= '1' after 60 sec;

end behaviour;

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  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    I rectified the error.

    Now however, when I run the code on the FPGA , even though according to the code the LED should light up after 20 seconds, the LED is lit from the beginning.
  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    The new code is -

    library IEEE;

    use IEEE.STD_LOGIC_1164.ALL;

    use IEEE.STD_LOGIC_ARITH.ALL;

    use IEEE.STD_LOGIC_UNSIGNED.ALL;

    entity timernew is

    port (clk : in std_logic;

    flag : out std_logic := '0' );

    end timernew;

    architecture Behavioral of timernew is

    begin

    process(clk)

    variable count : integer:=0;

    variable count1: integer:=0;

    constant int: integer :=(10**6);

    begin

    if(clk'event and clk='1') then

    count := count +1; --increment counter.

    if count = int then

    count := 0;

    else

    count1 := count1 + 1;

    if count1 > 1000 then flag <= '1' ;

    end if;

    end if;

    end if;

    end process;

    end Behavioral;
  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    Do the counters create registers? Check the RTL schematic. You have used a variable after updating it, which usually risks the synthesisor not creating a register for it. The best way to avoid this as a beginner is to always use signals, never variables.

  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    I changed the variables to signals, however still the LED glows instantaneously rather than waiting for 20 seconds and glowing.

    Is the structure of the IF statements correct ( Nested or not ) .
  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    Try changing

    if count1 > 1000 then flag <= '1' ;

    with

    if count1 > 1000 then flag <= '1' ;

    else flag <= '0' ;

    Did you assign the flag signal to the correct fpga pin?
  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    Changed as asked above.

    Also , pin assigned correctly.

    Still problem persists.

    Please help.
  • Altera_Forum's avatar
    Altera_Forum
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    12 years ago

    No test bench.

    Any idea regarding what could possibly be the source of error ?