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Altera_Forum
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15 years ago

Odd Counter Output.

Hello all;

I am trying to learn AHDL and have run into a problem. I tried searching the forum, but could not find anything like what I am seeing.

I am sure I have done something to the settings or something to cause the problem, because even with a new project I get the same results. The reason I think it is a setting is when I first simulated the code it worked correctly. I used it for a couple hours while using it in another file to compare it to so I could verify that my other code was working I started to get this output. It worked fine, but I never could get the other code to work right. I then made a new project and retyped the code, not just copied it with the same results.

I have made a simple counter. Below is the code:

SUBDESIGN TEST2

(

clock :INPUT;

Q[3..0] :OUTPUT;

)

VARIABLE

count[3..0] :DFF;

BEGIN

count[].clk = clock;

count[].d = count[].q - 1;

q[] = count[].q;

END;

I am not getting what I would expect, 15 to 0 repeating. What I am getting is this:

15,7,11,3,13,5,9,1,14,6,10,2,12,4,8,0

It keeps repeating. I did notice that all the numbers 0 to 15 are present.

I am using Quartus II ver 9.

Thanks for any help.

Larry

6 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Output is simply inverted.

    Try to change high and low levels and possibly reverse bit order and you'll get the right count.

    Cris
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Suggestion.

    If you don't yet know them, better to study Verilog or VHDL.

    AHDL is an old language not sure will be supported in the future.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    I second the recommendation to learn VHDL or Verilog. you cannot simulation AHDL in RTL form and lacks the portability and useful features of the other two.

    Was there any particular reason you picked AHDL? is your tutor stuck in the early 90s?
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    To Larry: your counter works fine, but you have the wrong order in your simulation showing Q[0..3] rather than Q[3..0].

    To Tricky: to a (self-)starter AHDL is much more intuitive then VHDL or Verilog. But is less high-level than the other 2, so nplttr's recommendation certainly is good advice.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Thank you all for your replys. AHDL is wha the coures instuctor wants. I have heard that AHDL may be on its way out. When done with this course I will learn VHDL.

    I will give the suggestions a try. Thank you again.
  • Altera_Forum's avatar
    Altera_Forum
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    15 years ago

    Thank you all for your replies. Cris72 and josyb where correct. In the .vwf file I had the MSB and LSB's reversed. Thank you both for your help. It saved me alot of trouble!!