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Buses

As circuits get more complicated, so do the schematics. To simplify the drawing, buses can be used. Buses should be used when you have a large group of signals that need to be routed together. For example, if we have a 32-bit address system, we will need 32 address lines to be routed around together. In this case, a bus line can be easier to draw and easier to follow for the reader. Another case where buses are useful is when there a large number of control signals that are generated and routed randomly about a sequential circuit. In this case, once the signal is on the control bus, it can be accessed anywhere without adding many new wires.

To get on or off a bus, a breakout device must be used. These can be created in LogicWorks by selecting New Breakout... from the Schematic menu. Like the module pin configuration, buses can be specified by groups of signals A3..0 or A0..3 or discrete signals separated by commas A0, A1, A2, A3.

Some words of caution with buses. Avoid the temptation to put everything on a single bus or try to use them for everything. The little red wires in LogicWorks are very useful for the reader who does not know the details of how your circuit works. Also be careful with your naming of signals on the bus. These names may colide with other signals that you are naming. Strange behavior in LogicWorks is usually a naming conflict between signals. I believe there is a character maximum for buses as well. I do not remember which version of LogicWorks the problem was part of, but only the first 8 or 16 characters of the signal name was used to identify it on the bus.

Here is a sample circuit that uses buses.

Last Modified: - Barry E. Mapen