Electrical – Simulating LPM_counter on Modelsim gives ‘z’ (high impedance) output


I'm trying to implement a simple 9-bit frequency divider using the LPM_counter Module.
Hardware and Software being used:

  • ALtera Max V-CPLD
  • Quartus II 64 bit Web Edition 15.0
  • ModelSim Altera Starter Edition 10.3d

I wrote a program in Block schematic format (BDF) adn downloaded it into the cpld and it works fine, giving the desired output. However when I try to simulate it in ModelSim it gives 'z' (high impedance) on all outputs.

For the simulation I created a Verilog file from the BDF file using the 'Create HDL design file fron current file' option in Quartus. Then I wrote A testbench to simulate a clock input for the LPM_counter module.

I've tried a lot of different things that I've read from different forums such as trying to run it without a testbench by giving a Clock input directly in ModelSim, trying reg outputs instead of wires and vice versa, amongst other things.

I've been stuck on this for a while now and really need it to work because I'll be needing ModelSim to make programs for some upcoming projects. I'm doing this to get used to the whole process before I actually work on it.

Btw I made a frequency divider using JK flipflops and that worked fine on both, the cpld and ModelSim simulation. Its just this black box module that I'm having problems with.

Source File (Converted to Verilog from .bdf)

module ninebitlpm(  myclk,  q );

input wire  myclk;
output wire [8:7] q; // only using the two most significant bits
wire    [8:0] q_ALTERA_SYNTHESIZED;

lpm_counter b2v_inst(   .clock(myclk),  .q(q_ALTERA_SYNTHESIZED));

assign  q[8:7] = q_ALTERA_SYNTHESIZED[8:7];


module lpm_counter(clock,q);

/*synthesis black_box */
input clock; output [8:0] q;



`timescale 1us/1ns

module test_lpm();

reg myclk;
wire [1:0]q;

ninebitlpm mycounter(myclk, q);

initial begin myclk = 1; forever #1 myclk = ~myclk; end


Best Answer

module lpm_counter(clock,q); is an empty black box.

To get it to simulate, you will need to use the actual HDL rather than the black box. There are two options:

  1. You can delete that module declaration and instruct Modelsim to compile the HDL file that was produced when you used MegaWizard.

  2. Copy the contents from the HDL file from (1) into your source file to replace the black box.