Logisim News

Logisim, a graphical design and simulation tool for logic circuits, is now at version 2.4.0. While this release includes several bug fixes, there are three major highlights: a Russian translation, improved support for latches, and command-line verification. The Russian translation includes all internal strings except the documentation. They are generously provided by Ilia Lilov, a student at Moscow State University of Printing Arts.

The support for latches involves a backwards-incompatible change in the behavior of the AND/OR/NAND/NOR gates: They now exhibit short-circuiting behavior, so for example, if any input to an AND gate is 0, then the output will be 0 even if some other inputs are the error value or are floating. Also, these gates emit an error value if all inputs are left unconnected. While this could break backwards compatibility for some circuits, it appears to reduce the oscillation errors that one would encounter when attempting to build a simple R-S latches using two NOR or two NAND gates - such simple circuits did not work properly before. Thanks very much to Brandon Whitehead, a teaching assistant at Georgia Tech University, who worked hard to identify the problem and experiment with ways to address it.

Finally, the new version adds support for executing circuits from the command line, without any graphical user interface. This can help with verifying that a circuit works correctly as modifications are made - and perhaps just as importantly, it can help instructors with grading. The section "Command-line verification" in the documentation explains this in further detail.

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/.