UMBC CMSC 313, Computer Organization & Assembly Language, Fall 2001, Section 0101

DigSim Information

DigSim is a Java applet that simulates simple digital circuits. DigSim was written by I. van Rienen and was released into the public domain (so it's free). The code is apparently not maintained by anyone anymore. In fact, the web page most often referenced as the place to get DigSim is no longer active.

There are several advantages of DigSim over B2Logic. First, DigSim is free. I also like the fact that the wires are colored to show which ones are high (red), which ones are low (green) and which ones are disconnected (gray). The disadvantages of DigSim compared to B2Logic are that DigSim has fewer features and it is harder to set up the system to allow the user to save a schematic (see below).

Start DigSim Now.

Running DigSim with Standard Examples

DigSim comes with a suite of standard examples. To run DigSim and play with these examples, all you need is a Java-enabled browser and point it at the start page for DigSim. Then, wait a few moments for the Java virtual machine to start up (actually could be quite long). You should get a new window with titled "Digital Simulator" ( like this). You should also see some new menu items either in a menu bar attached to the window or in the operating system's menu bar (this is OS dependent). Anyway, find the "File" menu and select "Open example". You should see a list of examples. Select one (e.g., "Flip Flop made with two NOR ports") and press "OK". DigSim should now load the circuit you selected (e.g. an SR flip flop). To start the simulation, press on the lightning symbol . Now you should be able to play with the circuit by pushing on switches, etc.

Using DigSim to Design Your Own Circuits

DigSim can also be used to design your own circuits. The catch is that most web browsers do not want to let a Java applet write to the disk. (This is usually a very good idea.) There are two ways to work around this:
  1. Convince your web browser that you really want to allow the DigSim Java applet to write to your disk. Some browsers will let the applet write to your disk if the applet is stored on the disk or executed from an appletviewer. You should download the entire DigSim package (181k tarred and gzipped) if you want to run the applet locally.
  2. Another method is dispense with the browser or applet viewer and run DigSim as a Java application. This requires a wrapper. I included one called "DummyAppletContext" in the DigSim package. The instructions to do this differ from system to system, depending on how Java applications are executed. In Unix (you have to be logged into the console), from the DigSim directory type:
         java DummyAppletContext DigSim -width 300 -height 50 fileop true
    You should get the usual DigSim window, but now it's running as an application and not an applet so you should be able to save. This was tested on the Dell computers in the PC labs booted into Linux.

In either case, try saving before doing anything too complicated. If saving files is prohibited, you'd get a Java exception error of some kind.

Last Modified: 16 Nov 2001 13:47:41 EST by Richard Chang
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