unpredictable led output on nexys2 board

Discussion in 'VHDL' started by iamonion, Feb 15, 2011.

  1. iamonion

    iamonion Guest

    Hi everyone!
    I'm learning to design PWM with nexys2 board and i've encountered very
    strange problem,
    I have one PWM that drives two LED-s, i program synthetised design by
    JTAG and everytime i load it, i observe one of two possible results:
    first... the expected one led 7 and led 4 lights up slowly, leds 6 and
    5 are off as in code below:
    led(3 downto 1) <= pwm_out & pwm_out & pwm_out ; -- these leds work
    always ok
    led(0) <= slowclk; -- this led is ok too
    led(7 downto 4) <= pwm_out2 & '0' & '0' & pwm_out2;
    But sometimes led 7 has inverted driving so it is on at beginning and
    dims out and what is more weird led 6 is on, but it should be off,
    there's no special signal just '0' specified. There's also some self-
    test flashed to board, it's LED's work always as intended.
    Clock frequency of PWM is 50MHz.
    What could cause this problem?
    Thanks.
    Juraj Galbavy
     
    iamonion, Feb 15, 2011
    #1
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  2. iamonion

    iamonion Guest

    Hello,
    I think i've solved my problem by moving one jumper pin from position
    slave serial to JTAG.
    Now after reset the default test is not run and i can transfer
    configuration many times with
    no defects on LED outputs, yet.
    As i realised before changing jumper, any design i tried to run had
    some chance to have led 7 and 6
    outputs to be inverted both at the same time.

    Juraj

    On 16 ún, 00:47, iamonion <> wrote:
    > Hi everyone!
    > I'm learning to design PWM with nexys2 board and i've encountered very
    > strange problem,
    > I have one PWM that drives two LED-s, i program synthetised design by
    > JTAG and everytime i load it, i observe one of two possible results:
    > first... the expected one led 7 and led 4 lights up slowly, leds 6 and
    > 5 are off as in code below:
    >         led(3 downto 1) <= pwm_out & pwm_out & pwm_out ; -- these leds work
    > always ok
    >         led(0) <= slowclk; -- this led is ok too
    >         led(7 downto 4) <= pwm_out2 & '0' & '0' & pwm_out2;
    > But sometimes led 7 has inverted driving so it is on at beginning and
    > dims out and what is more weird led 6 is on, but it should be off,
    > there's no special signal just '0' specified. There's also some self-
    > test flashed to board, it's LED's work always as intended.
    > Clock frequency of PWM is 50MHz.
    > What could cause this problem?
    > Thanks.
    > Juraj Galbavy
     
    iamonion, Feb 16, 2011
    #2
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