Specifications

Using Subcircuits 57
designs, then click the Attach button. The selected design will now be
brought to the front. Close its window. If the Update/Revert/Cancel
option box appears, select Update.
The subcircuit is now attached to the parent symbol and has ceased to exist
as an independent design.
Creating a Subcircuit—Bottom–Up
In a bottom–up design process, we create the subcircuit first then use it to
define the pins on the parent symbol. In LogicWorks, this is easier than the
top–down procedure because we can take advantage of some of the auto-
matic features of the device symbol editor for this purpose. The bottom–up
procedure is as follows:
 If you are creating the subcircuit from scratch, select the New Design
command from the LogicWorks menu bar to create a new circuit
window, then use the schematic drawing tools to draw the circuit. You
may use any existing parts in creating the subcircuit, including other
subcircuit devices. Alternatively, if the subcircuit is to be based on an
existing circuit file, open that file using the Open Design command.
 If you haven’t already done so, add Port Connectors corresponding to
the pin connections on the symbol, as described in the previous section.
 Leave this circuit open (that is, displayed in a circuit window). You
may save this circuit to a file if desired, but it is not necessary to
perform this procedure.
 Open the device symbol editor. Select New in the File menu and then
choose the Device Symbol option. From the Options menu, select the
Subcircuit / Part Type command and choose the “Create a subcircuit
symbol and store the subcircuit with it...” option. Select the subcircuit
that you just created from the list of open windows that is presented.
Close the PartType configuration dialog. You will notice that symbol
editor has extracted the names from the port connectors in the
subcircuit and placed them in the Pin List at the left side of its own
window.
 Create the graphics for the symbol using either drawing tools, the
Autocreate Symbol command in the Options menu. Every pin listed in
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