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In order to internally represent the netlists and their corresponding
component connectivity, the Tcl/Tk script employs several
global associative arrays. The array names, their indices and their
contents are shown in Table 3.6. Notice that all
associative arrays which are indexed by point identifiers are prefixed
with pnt, whereas associative arrays indexed by netlist
tag names are prefixed with net.
Array Name
Array Index
Array Contents
pnt_coord point identifier (x,y) coordinates of the
point.
pnt_wires point identifier List of wire identifiers
adjacent to the point.
pnt_port point identifier Canvas identifier of the port
connected to the point
(if applicable).
pnt_label point identifier Canvas identifier of the
textual label for the point
(if applicable).
net_ports netlist tag name List of ports connected
to a netlist. Each element
of the list is a pair
consisting of a port type
and the point identifier
connected to the port.
net_name netlist tag name The textual name of the
netlist as assigned by the
user via the
Netlist Label
dialog box.
Table 3.6: Netlist Representation Arrays
As an example of how netlists are represented internally, consider the
incomplete circuit displayed in Figure 3.9. Remember that all
newly created canvas items are assigned unique numeric identifiers so
that they may be referenced later on. However, for clarity, capital
letters will be used to represent point identifiers, integers will
represent the identifiers of wire segments and lowercase letters will
represent port identifiers (that is, the identifiers of port
rectangles). A shaded port indicates that the port has been connected
to the overlapping point. The sans serif font represents netlist
labels placed on the workarea by the user via the Netlist
Label dialog box; the numeric identifier assigned to this text label by
Tk will be represented by the notation id(label).
[画像:figure1754]
Figure 3.9: Example of a Circuit Layout
The tags for each of the points and wires for this circuit are shown in
Tables 3.7 and 3.8 respectively. Note that all
points have been given the point tag and all wires have been
given the wire tag. Also note that in addition to the
netlist tag, all wires and points have been given a special
netlist identifier tag name which serves to indicate to which netlist
the wire or point belongs.
Point Identifier List of Tags
A { point netlist netlist_0 }
B { point netlist netlist_1 }
C { point netlist netlist_2 }
D { point netlist netlist_0 }
E { point netlist netlist_1 }
F { point netlist netlist_3 }
G { point netlist netlist_3 }
H { point netlist netlist_3 }
I { point netlist netlist_3 }
J { point netlist netlist_2 }
K { point netlist netlist_4 }
L { point netlist netlist_3 }
M { point netlist netlist_4 }
Table: Point Tags for the Circuit in Figure 3.9
Wire Identifier List of Tags
1 { wire netlist netlist_0 }
2 { wire netlist netlist_1 }
3 { wire netlist netlist_2 }
4 { wire netlist netlist_3 }
5 { wire netlist netlist_3 }
6 { wire netlist netlist_3 }
7 { wire netlist netlist_3 }
8 { wire netlist netlist_4 }
Table: Wire Tags for the Circuit in Figure 3.9
next up previous contents
Next: Point Arrays
Up: Netlist Modules
Previous: Dynamic Netlist Identification
Donald Craig
Mon Jul 8 12:05:35 NDT 1996
