Appendix: Logisim Tips

This appendix contains some helpful Logisim tips and pitfalls to avoid.

Wiring

If you want to know more details about each component, go to Help -> Library Reference for more information on the component and its inputs and outputs.
Use tunnels! They will make your wiring cleaner and easier to follow, and will reduce your chances of encountering crossed wires or unexpected errors.
Ensure you name your tunnels correctly. The labels are case sensitive!
You can hover your cursor over an input/output on a component to get slightly more information about that input/output.

Your circuits should always fit in the provided harnesses. This means that you should not edit the provided input/output pins or add new ones. To ensure your circuit fits int he harness, you can open the harnesses in the harnesses folder and check that there are no errors.
Don't create new .circ files. You can make additional subcircuits if you want, but they must be in existing files.

Note that if you modify a subcircuit, and another circuit file uses that subcircuit, you will need to close and re-open the outer circuit to load the changes from the subcircuit. For example, if you modify imm-gen.circ, you should close and re-open cpu.circ to load your changes.
When modifying a subcircuit, you should always open up the subcircuit file. For example, you should modify imm-gen.circ, not the imm-gen subcircuit in cpu.circ.

The clock input signal (clk) can be sent into subcircuits or attached directly to the clock inputs of memory units in Logisim, but should not otherwise be gated (i.e., do not invert it, do not AND it with anything, etc.).
We recommend not using the Enable input on your MUXes. In fact, you can turn that attribute off (Include Enable?). We also recommend that you disable the Three-state? attribute (if the plexer has it).