## Getting Started with Digital Works

Digital Works 2.0 is a circuit simulator for Windows 95 written by D. J. Barker at the University of Teesside. This is a freeware program. You may use it without any obligation, and you may give unmodified copies of it to others. You can find out about the current version of Digital Works (not free) at their home page. You may want the licensed version if you get deeply into logic design. The freeware version is sufficient for CS272 and CS333.

Download the Digital Works installation file. This 800K zip file, digwork.zip, contains DW20_95.exe, a self-extracting install file. Run it to install Digital Works under Windows 95/NT/2000/XP. You can erase the install file when the installation is complete.

Download the sample circuit from the Designing Combinational Circuits handout by left-clicking on the link. Save the file as "sop.dwm" in a directory you have set up for your circuit simulations.

Start Digital Works and open file "sop.dwm" using the File menu.

Start the simulator by pressing the "run" triangle at the left end of the third toolbar, if it isn't already depressed. Since this is an interactive circuit, and not one driven by a clock, nothing much will happen until you cause it to.

Select the Interactive Input, or "hand" tool by pressing the "hand" button on the toolbar. The cursor will change to a hand shape.

Place the "hand" cursor over one of the input buttons, A, B, or C, at the lower left of the circuit and change its state by left-clicking. Notice how the state of the variable and its complement change as shown by the LED's at the top of the circuit. Observe whether the output, F, changes state. Now run through all eight possible combinations of A, B, and C in binary number order. (Use the truth table in the handout to see which variables change at each step.) Check that the output, F, reflects the value specified in the truth table. (It does, so this circuit computes the Boolean function specified in the truth table in the handout.)

Now you are ready to try a circuit of your own. Download sopframe.dwm by left-clicking the link. Open this file in Digital Works. You will see that is is a sum-of-products circuit design, but the AND gates aren't wired. Pick a circuit from among the ones we drew in class; you will wire the AND gates to simulate this circuit.

Select the pencil tool and place the cursor on the topmost input of the first AND gate. When the curson is positioned correctly, the word "Wire" will appear within the cursor. Left-click once and release. Move the cursor to the left. You will be dragging a wire from the AND gate. Position the cursor over the correct vertical wire. When the word "Wire" appears, left-click once and you will have constructed a wire to the AND gate. Wire the remaining gate inputs. If you make a mistake, get the pointer tool, click the incorrect wire with it, and press the Delete key.

You do not have to use all four AND gates if the function you are simulating has fewer than four product terms. Similarly, if you are simulating a function of two variables, you can ignore the wiring for C and its complement. However, the number of inputs on each AND gate must be correct; if there is an unwired input, the AND gate will never produce output. To change the number of inputs, use the pointer tool. Right-click the AND gate you want to change and use the menu to change the number of inputs.

Test your circuit by running through all the possible input values, using the truth table as a guide. Verify that your circuit computes the function described by the truth table.

You can clean up your circuit by using the pointer tool and the delete key to get rid of unused components.

Now try simulating one of the multi-level circuits from the text. Start with a blank workspace and arrange gates, inputs, and LEDs by selecting them from the middle toolbar and left-clicking to place them in the workspace. Wire your circuit with the pencil tool and test it by cycling through all values of the inputs.