# How to view wire values in Altera Quartus Prime

I would like to be able to view waveforms showing internal nodes in a circuit specified in Verilog in Altera Quartus Prime. I am having trouble doing so when a wire is an output of one module and an input of another. For example, my top-level entity includes:

module cpu(input [9:0] SW, output [9:0] LEDR);
wire [7:0] pc_in;
wire [7:0] pc_out;

assign LEDR[7:0] = pc_out;

pc my_pc(pc_in, SW[9], Continue, pc_out);     // pc_out is an output
instruction_memory mem(pc_out, instruction);  // pc_out is an input
endmodule


(There's more, but I left out irrelevant parts.)

Here is the full definition of pc:

module pc(data, clock, enable, q);
input [7:0] data;
input clock;
input enable;
output [7:0] q;
reg[7:0] q;

always @ (posedge clock)
begin
if (enable)
q <= data;
end
endmodule


While I can find pc_out in the Node Finder and add it to my waveform in the Simulation Waveform Editor, it shows up as an input:

Note that it is logically equivalent to the LEDR output.

I tried changing the type of pc_out from INPUT to BIDIR, BURIED, COMB, OUTPUT, and REG, to no effect. (The only difference is the initial values.)

Whatever type value I set it to, that is how it appears in the output waveform shown after functional simulation:

The same thing happens if I add the q output of my_pc (which is a basic register) and is equiavlent to pc_out.

I've successfully viewed signals by connecting them to outputs, but the chip I'm simulating only has 10 LEDs. (I'd be willing to switch to another real or fake chip with a huge number of outputs, if that's the best solution.)

• What does the interface to pc look like? In particular, what is the type of the second port (SW[9] in your code)?
– user39382
Nov 14 '16 at 2:57
• Thanks for looking at this, @duskwuff. I've added the contents of pc.v to the connection. I'm using SW[9] as a clock. Nov 14 '16 at 3:01
• Is anything forcing Continue?
– user39382
Nov 14 '16 at 3:05
• @duskwuff Continue is sometimes low, sometimes high, as verified by a simulation with an LED assigned to it. The value of Continue is assigned a Boolean function of two other signals. Nov 14 '16 at 3:10
• By what? There's nothing driving that signal in any of the code you've included.
– user39382
Nov 14 '16 at 3:23