Specifications

50 Chapter 3—Advanced Schematic Editing

Following is a short summary of the rules governing subcircuit devices.

More information on each of these topics is included in the following sec-

tions.

 The “pins” on the subcircuit device symbol represent connections to

specific input–output points on the internal circuit. A “port connector”

pseudo–device must be placed in the subcircuit corresponding to each

pin on the parent symbol. Port connector symbols are found in the

connect.clf library supplied with LogicWorks.

 A subcircuit device can be opened at any time by double–clicking on

the parent symbol. Subcircuits can be “locked” to prevent accidental

modification by selecting the Lock Opening Subcircuit option in the

Device Info box.

 Subcircuits cannot be “recursive,” i.e., you cannot use a device symbol

inside its own internal circuit.

 The netlist and bill of materials reports generated by the Report tool in

LogicWorks only list components in the top–level circuit in the design.

Devices in subcircuits are never listed.

 A device symbol with an associated subcircuit can be stored in a part

library. Each time that symbol is selected from the library, the

subcircuit definition will be loaded and attached to the device.

 When you open a device’s subcircuit, a temporary copy of the

subcircuit is made to isolate it from all others of the same type that

have been used elsewhere in the design. When you closed the

subcircuit, choosing the “update” option will cause all other devices of

the same type to be modified.

 If a given type of subcircuit device has been used more than once in the

same design, you can only have one of them open at a time for viewing

or editing the subcircuit.

 Signals in an open subcircuit can be displayed in the Timing window.

As soon as the subcircuit is closed, the waveforms for any of its signals

that were displayed will be removed.

A Simple Subcircuit Example

The following diagram is the master circuit, or top level, of our design

example:

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