Logisim, a graphical design and simulation tool for logic circuits, is now at version 2.3.0. Among the many changes for this release are a very different interface for working with tools and a largely rewritten set of built-in libraries.
The new tool interface collapses the Select Tool and Wiring Tool from previous versions into a single tool, called the Edit Tool, which identifies whether the user wishes to select components or add wires based on whether the mouse is over a point where a wire is likely to be added. (The user can press the ALT key to toggle the wiring/select choice.) Also, when the user adds a new component such as an AND gate, the program automatically reverts back to the Edit tool with the added component selected, so the user can then move the component or add new wires to it. The user can use the new Duplicate option in the Edit menu (or Control/Command-D) to add additional copies of the component. (The Preferences window allows a user to customize Logisim to use the old behavior of remaining with the new-component tool.)
Also notable in this new version is a thoroughly revamped API for developing components in Java. Most built-in libraries have been rewritten to use this API instead - and to expand the functionality by adding new components: Priority Encoder, Shifter, Counter, Shift Register, and Random. Moreover, this version allows the user to choose the XOR gate behavior (whether it emits 1 when an odd number of inputs are 1 - or only when exactly one input is 1, as it has in the past), and it adds new options for the RAM gates. Moreover, a new project option allows the user to specify that the built-in gates should have an error output whenever any of the inputs are disconnected or floating; this is to accommodate users unhappy with Logisim's default treatment, which doesn't match how gates work in practice.
Besides these major changes, there are numerous minor changes. One will immediately notice that most built-in libraries are now loaded by default. When multiple components in the circuit are selected, all attributes the components hold in common are displayed and available for alteration. The Export Image dialog allows the creation of PNGs and JPGs in addition to GIFs. And the font and color dialog boxes have been replaced with nicer third-party dialogs.
Educational institutions around the world use Logisim as an aid to
teaching about digital logic and computer architecture. As a Java
application, Logisim can run on most major operating systems. Read more
about Logisim at http://www.cburch.com/logisim/, and download it from
SourceForge.net at http://sourceforge.net/projects/circuit/.
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