CIRC File

A .circ file is a Logisim Circuit file, an XML-based description of a digital logic circuit used by the Logisim circuit simulator. Logisim was originally developed by Carl Burch around 2001 as an educational tool for designing and simulating combinational and sequential logic. After Burch retired the project in 2014, the community fork Logisim-evolution became the recommended successor, actively maintained by EPFL and open-source contributors.

A .circ file is plain XML rooted at <project source="version">, containing one or more <circuit> elements. Each circuit holds <wire> elements (defined by pixel-grid coordinates), <comp> elements representing logic gates, flip-flops, pins, and other components with attribute settings, and optionally <vhdl-entity> blocks for HDL-backed components. The source attribute in <project> records the Logisim or Logisim-evolution version that created the file. Files produced by Logisim-evolution are not backward-compatible with the original Logisim 2.x.

Logisim-evolution extends the format with chronogram (timing diagram) analysis, FPGA export targeting Xilinx, Altera, and Lattice boards, VHDL and Verilog co-simulation, multi-bit bus wiring, and expanded gate libraries. .circ files are widely used in undergraduate CS and EE courses (UC Berkeley CS 61C, MIT, ETH Zurich). The format is human-readable XML and can be opened in any text editor, though meaningful editing requires the Logisim-evolution graphical interface.