I've been trying to get my Cyclone II FPGA (from the Starter Kit, EP2C20) to work. I've gotten the Quartus II software to work on my Ubuntu setup and it' ALMOST working - I can write some Verilog, compile it, and put it on my device via the programmer. However, I can't get my code to control the FPGA outputs in any meaningful way. Here is, essentially, the code I'm trying:

module fpga(output LEDG[7:0);

assign LEDG = 1;


I want all the green LEDs on the FPGA to light up. What am I doing wrong?

Terribly sorry if this is something I could've Googled, I just spent the past hour trying to but didn't get too far (there doesn't seem to be much example Verilog code made for FPGAs out on the internet, at least any code which deals with minutiae like activating LEDs).

I can't wait to get started playing with this thing for real, so would appreciate any help getting this minor step working!

Update: The Quartus II Pin Planner is showing that the Fitter Location for the pins I care about is different from the pins specified in the datasheet. How can I fix this without manually re-assigning all the pins to the right places?

  • 2
    \$\begingroup\$ You will have to manually assign the pins, otherwise the tools will pick randomly \$\endgroup\$ Aug 20, 2012 at 8:55
  • \$\begingroup\$ There should be a pin constraint file supplied with the starter kit that contains all the pin assignments (for pins used in the kit, anyway). \$\endgroup\$
    – Ben Voigt
    Aug 20, 2012 at 22:33

1 Answer 1


Your code is not quite right.

If you want to set something to a value, you need to create a register and set it accordingly, then assign the value to an output. Generally you cannot use initial statements for synthesis (check your documentation) so setting the register to a constant on a reset signal, or using a ROM block are options.
Let's say you want to flash the LEDs though, this is more exciting than just turning them on. Say we have a 16MHz clock, to slow the clock down so the LEDs flash visibly, we need to divide it down. If we pick a 24 bit count register, 16e6 / (2^24) = ~1Hz so LEDs will update once per second.

module fpga(
input clk,
output LEDG[7:0);

// output reg to set 
reg rOUT[7:0]
// counter reg to slow clock down
reg rCOUNT[24:0]

// this models the synchronous logic, the block is activated on each positive edge of clk
always(@ posedge clk)

// add one to rCOUNT on each clock positive edge
rCOUNT <= rCOUNT + 1;

    // if rCOUNT equals 0xFFFFFF then increment rOUT by 1
    if(rCOUNT == 24'hFFFFFF)
        rOUT <= rOUT + 1;


assign value of rOUT to LEDG so LEDs will light according to rOUTs current value
assign LEDG = rOUT;


Note that when assigning a value to a register, you need to specify the width otherwise it will default to the default width of the system (e.g. 32 bits)
So if you create an 8 bit register rOUT and you want to set it to all 1's, then assuming your sythesis software allows assigning an intitial value you would write reg rOUT = 8'b11111111; or reg rOUT = 8'hFF;
This will all become clear as you read more.

About the Quartus pin planner, I'm not sure (as I use Xilinx/Actel FPGAs), but make sure the pin assignments are correct. YOu should be able to either change them in the pin planner or manually edit the constraints file as necessary. It will all be there in the (no doubt very lengthy) documentation.

A good book is "FPGA Prototyping by Verilog Examples" (Pong P Chu), but there are some examples out there you can follow - fpga4fun is a good site with many example projects. Spend some time reading and getting to know the constructs of the language. Try stuff out in the simulator first to confirm correct operation before programming FPGA.


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