Hierarchy Block and Subcircuit Basics
By Lacy

Hierarchy Blocks and Subcircuits are basically the same thing with the big difference being how they are handled by Multisim. A subcircuit block is contained totally within the current design project while a hierarchy block is saved as a separate schematic on your drive.

You create a subcircuit by three methods.

1. Creating a window around the components and nets in your schematic to be included in the subcircuit and then going to PLACE>Replace By Subcircuit. This creates all the input and output connections automatically. You may have to rename them later to something more desirable as they are just generically labeled as IO1, IO2 etc. Caution: This removes the components from the main schematic and places them inside the subcircuit. You can always use the Undo command to revert it back in case you made an error. I would suggest to do this immediately after creating it otherwise you run the risk of not being able to restore the original portion of the schematic without doing a lot of cutting,pasting and rewiring. This is due to the Multlsim Undo buffer having a limited size.

2. Going to PLACE>New Subcircuit. This creates a blank box without any input or output pins. You must click the subcircuit box and select Edit HB/SC and then place your circuit inside with HB/SC connectors from PLACE>Connectors>HB/SC Connector.

3. Create the schematic of your subcircuit first, place the HB/SC connectors and then use the process outlined in step one. To create a Hierarchy Block you can use the same 3 techniques oulined above except you choose from the Place Menu -Replace by Hierarchy Block-, -New Hierarchy Block-. The difference is that this block will be saved as a separate file on the hard drive and can be re-used in other designs or editied at anytime by loading it as a separate Multisim scheamtic. Subcircuits are saved within the current project and cannot be re-used in other designs.

So what are they good for? The subcircuits can have many uses, but the one that I use them for most often is to shrink my print down to create a block diagram form. This compresses the design to fit in my work space. Also, you could start out using subcircuit blocks to outline the block diagram for design flow purposes and then go into each subcircuit and create the circuit that accomplishes this particular block. There may be other applications for these, but this is mainly what I have used them for.

The Hierarchy blocks are more versatile in their applications. Once you create a circuit that may be used across more designs, then this will always be available to you to use from the hard drive. You could have a complete library of common circuits and then just choose the one you need and place it in the current design. This makes it easier to design things as you do not have to re-create circuits that have already been designed and tested. Call it Plug and Play Multism style.

You can also create components using the Hierarchy Blocks. This is not like using the Component Wizard, but is an alternative when you need a quick and dirty component for your design. This is the only method of component creating that allows the use of Interactive Components to be used in the creation of new parts.

Now for the downside of Hierarchy Blocks/Subcircuits. You cannot assign footprints to them for export to Ultiboard as a single component. All the components inside the subcircuit/hierarchy block will transfer as individual parts. If you need to export your subcircuit/hierarchy block as a single component to Ultiboard you will need to use the Component Wizard to create a blank component template with a footprint. Once the simulation phase is done you will need to replace the subcircuits in your schematic with the blank component templates in order to transfer your schematic to Ultiboard in this manner.

What I have outlined here is just the basics for these items. There may be more uses for them other than what I have outlined here. I only want to give the basics and you may have a completely different use for them. It is up to the designer and the application to determine how to use them and when.