CSE467: Advanced Logic Design

Winter 2000

Lab 5

Due by the beginning of Lab 6.

Overall Description

In this Lab assignment you will be displaying an image which has been loaded into memory, on a monitor using the VGA interface that you have designed.  You will then add a circuit that displays a "cross-hair" on top of the image on the screen.  The position of the crosshair can be moved by pressing keys on a keypad.

Part I - Test the VGA interface

To use the VGA interface that you have designed, you need to connect it to the pins connecting to the VGA cable and to the pins connecting to the memory. First, take a look at the schematic from the XS40 documentation.  The project test.zip (NOT lab5.zip) in ifilesrv1/courses/cse467/winter00 contains a skeleton project for this lab.  This project has a top level schematic and two macros. To get to the schematics for the macros, use Open Macro under the File menu. You will want to edit the schematic for the VGA macro to contain the circuit that you designed. The top level schematic must also be changed to contain the symbols (macros) for these two schematics. Symbols for these schematics can be found in the project library.

You will notice that the schematics contain no pin names. Instead, in this project the pin assignments are made in a UCF file called test.ucf. Obviously, it is important that the UCF file have the same name as the project. This file can be found in the project manager. Take a look at this file and you will see that most of the Xilinx chip pins appear along with a comment saying what pin is connected to it on the board. You should compare this to the schematic from the documentation to see how the pin numbers match up.  Notice that the names used for the VGA and memory pins in the schematics appear here along with the appropriate pin numbers. You can use either the UCF file or pin numbers in the schematic to specify the pin numbers, but from now on we will use the UCF file.

Please use the circuit that you designed for the VGA interface.  Only use the solution if you had MAJOR problems with your own.  For reference, this solution is in lab5.zip at the same location of test.zip. Compile your project to produce a BIT file.  To try out your project, you will first have to disconnect the wires from Lab 4, which used the VGA and memory pins for other things.  Next connect the monitor, the pc and power up the board. Now you will have to do three downloads, one to load a design into the chip that is capable of filling the memory, one to get the image into the memory, and the third to download your design:

  1. xsload xsramvga.bit
  2. xsram mazefile.bin
  3. xsload foo.bit
The mazefile.bin, xsramvga.bit and xsram.exe files can be found in the same directory as the test.zip project. The image should now be visible on the screen.  If you have problems, you can use the logic probe to check that pins have the right values or the logic analyzer.

Part II - Connect up the keypad

We will be using the keypad as an input device for the project.  The keypad has 16 keys which are connected to the 9 pins as follows.  There are four wires that run vertically, one for each column, and four wires that run horizontally, one for each row, for a total of 8 wires.  Each of these wires is connected to a pin.  When a key is pressed, the row wire and the column wire for that key are connected to the 9th pin, which is called a common pin.  To use the keypad, you connect the 8 pins for the row and column wires to Vdd through a 4.7K resistor, and you connect the common pin to GND.  The 8 pins are thus HIGH when no key is pressed, and one pin in each set of four goes LOW when a key is pressed, indicating which key has been pressed.  Instead of using 8 discrete resistors, it is easier (no wires!) to use a Resistor Pak, which contains 8 (or 10) resistors, each connecting one pin to a common pin which is connected to Vdd.

Connecting things up will take a little detective work.  You will have to figure out which pins are which on the keypad, then figure out which pins are which on the Resistor Pak.  When you have finished connecting things up, you will need to connect the 8 keypad pins to the FPGA along with the reset button, although you could use one of the keys on the keypad instead of the pushbutton switch.  You may use pins 6, 7, 8, 9, 14, 27, 29, 68 and 75 which are connected to the microprocessor that we are not using.  You will recall from last week that thes kind of switch tends to bounce.  Unfortunately, we cannot use last week's method to debounce the keys.  Instead we will look at the keypad only once per frame, which will avoid problems with any bouncing in the keys. In the next part, you will have to add the input pads and buffers for these signals and add the appropriate entries to your UCF file.  You can look at the way the other pads are connected to see how this is done.

Part III - Adding a Crosshair

We're now going to add a crosshair to the display that will be on top of the image displayed from memory.  We will use registers to keep track of the row and column location of the crosshair, which will be displayed as a horizontal and vertical line.  That is, we will display two white lines, one on the row and one on the column position of the crosshair.  You will have to design a circuit that displays the crosshair on the screen at this location, which can be changed using the keypad. This circuit should not be added to the VGA interface.  Instead, it should be added to the top-level schematic, as a symbol representing either a Verilog module or a schematic.  The crosshair will be controlled using the keypad.  Pick four keys that you can use to change the location of the crosshair (up, down, left, right).  Design a circuit that will check the keypad once per frame, and increment/decrement the row or column according to which key is pressed.

Extras!

If you would like to try more, here are some ideas (for small amounts of extra credit - I want you to do this because you have the time and it's fun, not because you need the points).
  1. Display something more interesting than two lines at the crosshair location.
  2. Use more keys so that you can move the crosshair diagonally.
  3. Have the crosshair move slowly at first, and then faster if the key is held down.
  4. Display a larger image using fewer bits per pixel than 8.  (Talk to us about the image file format.)
  5. Your own idea (but talk to us first!)

Hand In:

ebeling@cs.washington.edu