Learn Verilog by Example

I did not initially plan on adding such topics to this blog but the reason I'm covering this is because I had a great deal of difficulty coding a FIFO buffer as I also was not clear regarding this concept. I was writing writing combinational logic in sequential blocks, which I read is not a good idea. In an always block expressions and variables can be connected using either a blocking or non-blocking statement. Knowing when to use which will make the code work. As a general rule blocking assignments are used to describe combinational logic and non-blocking are used to describe sequential logic. Blocking Assignment: Simply put this follows more of a C and C++ style, that is the lines of code are processed one after an other. The syntax for this blocking assignment is: (variable) = (expression); So when this line is executed the expression on the right hand side is calculated and the value is assigned to the variable on the left hand side. While this expression is b...

Now that we have the blinking LED in Verilog up and running, we can do an advanced version of the same project; a binary counter using the LED's. Also this time I will be using the push button to increment the counter. So every time the push button is pressed the counter will be incremented by 1, the LED's will present the binary counter. The code for the program is shown below: module button_binary( input clock, input reset, input button, output led, output led2, output led3, output led4, output led5, output led6, output led7, output led8 ); reg [7:0]count; always @ (posedge button or posedge reset) begin if (reset) count <= 0; else if (button) count <= count + 1; end assign led = count[0]; assign led2 = count[1]; assign led3 = count[2]; assign led4 = count[3]; assign led5 = count[4]; assign led6 = count[5]; assign led7 = count[6]; assign led8 = count[7]; endmodule The above program is so simple it ne...

This is a very simple program, the desired target is to make the LED's on the BASYS2 board blink, and by blinking I mean a very visible turning on and off. This can be very easily achieved in verilog. The code can be found below: module led_simple( input clock, input reset, output led, led2, led3, led4, led5 ); reg [26:0] count; //A sizable 27 bit register so that the blink can be seen and is visible, too small a register will make the //register stay on as it will blink extremely fast. always@ (posedge clock or posedge reset) begin if (reset) count <= 0; //if reset button is pressed, initialize or reset the register else count <= count + 1; //otherwise increment the register end assign led = count[26]; //MSB connected to output led. and the other outputes conncted as below assign led2 = count[25]; assign led3 = count[24]; assign led4 = count[23]; assign led5 = count[22]; endmodule The concept is very simple. I defined a 27 b...

Here is the user constraint file (.ucf) file that shows every pin location on the board. This file will be used in every project here as without it programming the FPGA is impossible. # Pin assignment for LEDs NET "ld " LOC = "g1" ; NET "ld " LOC = "p4" ; NET "ld " LOC = "n4" ; NET "ld " LOC = "n5" ; NET "ld " LOC = "p6" ; NET "ld " LOC = "p7" ; NET "ld " LOC = "m11" ; NET "ld " LOC = "m5" ; # Pin assignment for slide switches NET "sw " LOC = "n3"; NET "sw " LOC = "e2"; NET "sw " LOC = "f3"; NET "sw " LOC = "g3"; NET "sw " LOC = "b4"; NET "sw " LOC = "k3"; NET "sw " LOC = "l3"; NET "sw " LOC = "p11"; # Pin assignment for pushbutton switches NET ...