Specifications
24 Chapter 2—Schematic Editing
Signal names are known throughout a schematic page. Like-named
signal lines are thus logically connected for simulation and netlisting
purposes. Whenever a signal name is added or changed, the circuit is
checked for a change in connectivity. If the name is now the same as
another signal, the two signals are merged into one. If this signal
segment was previously connected by name to others, and the name is
changed, then the logical connection is broken. Whenever a name
change causes two signals to be connected, the changed signal will
flash on the screen to confirm the connection.
Signals which are contained in busses are a special case. Every signal
contained in a bus has a name, even if it is not displayed on the
diagram. However, the names of bussed signals will not be used to
make logical connections unless an explicit name label has been added
to the signal line.
For example, if you have a bus containing a signal named CLK and a
separate signal line also named CLK, there will be no logical
connection between these two signals. The name appearing on the bus
breakout is part of the breakout symbol and is not considered to be a
name label. If an explicit label is added to the bussed CLK signal
(using the text cursor) then the two CLKs will be logically connected.
The same rules discussed above for signals also apply to busses.
Whenever two busses are logically connected, all like-named internal
signals also become logically connected.
Device Names
In this book, we use the term “device name” to refer to the character string
that identifies a unique device in the circuit. Typical device names might be
U23, C4, IC12A, and so on. This is distinct from the type name or part
name that is used to distinguish the type definition that is read from a
device library. Typical part names are 74LS138, MC68000L8, SPDT
Switch, and so on.
Adding a Device Name
Enter Text mode either by selecting the Text menu item in the Edit menu,
or by clicking on the text icon in the Tool Palette:
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