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<HTML><HEAD><TITLE>Using Electric 1-11: Schematics Example</TITLE></HEAD>
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<!-- PAGE BREAK --><A NAME="chap01-11"></A>
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<BR><CENTER><FONT SIZE=6><B>Chapter 1: INTRODUCTION</B></FONT></CENTER><BR>
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<CENTER><TABLE WIDTH="90%" BORDER=0><TR>
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<TD><CENTER><A HREF="chap01-10.html#chap01-10"><IMG SRC="../images/iconplug.png" ALT="plug" BORDER=0></A></CENTER></TD>
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<TD><CENTER><H2>1-11: Schematics Example</H2></CENTER></TD>
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<TD><CENTER><A HREF="chap02-01.html#chap02-01"><IMG SRC="../images/iconplug.png" ALT="plug" BORDER=0></A></CENTER></TD></TR></TABLE></CENTER>
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This section takes you through the design of some simple schematics.
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Electric starts in IC design mode (MOSIS CMOS layout),
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so you have to switch to schematics before doing any design.
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Use the <B>Change Current Technology...</B> command from the <B>Technology</B> menu.
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Select the "schematic, digital" entry (you will have to scroll down to find it) and click OK.
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The symbols in the component menu on the left will change to a Digital schematics set.
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Analog components can be created by selecting the "schematic, analog" technology,
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but they may also be selected with the <B>New Analog Part</B> command in the <B>Edit</B> menu.
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Before you can place any schematics, the editing window must have a facet in it.
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Use the <B>Edit Facet...</B> command in the <B>Facets</B> menu.
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This will show a dialog with a list of existing facets (which is empty, because none exist yet).
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Click on the "New Facet" button at the bottom of this dialog to create a new facet.
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You will then see a dialog which asks you for information about this new facet.
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</TD><TD><CENTER><IMG SRC="../images/chap01-03.png" ALT="Figure 1.3"></CENTER></TD></TR></TABLE>
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<TD><CENTER><IMG SRC="../images/chap01-24.png" ALT="Figure 1.24"></CENTER></TD><TD>
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Type the name ("MyCircuit" is used here) and click OK.
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The editing window will no longer have the "No facet in this window" message,
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and circuitry may now be created.
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Logic elements are placed by selecting nodes from the components menu,
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and then wiring them together.
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This example shows two nodes that have been created.
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This was done by clicking on the appropriate component menu entry,
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and then clicking again in the editing window to place that node.
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After clicking on the component menu entry,
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the cursor changes to a pointing hand to indicate that you must select a location for the node.
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When placing the node, if you press the button and do not release it,
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you will see an outline of the new node,
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which you can drag to its proper location before releasing the button.
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</TD><TD><CENTER><IMG SRC="../images/chap01-17.png" ALT="Figure 1.17"></CENTER></TD></TR></TABLE>
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the top node is called a Buffer (found in the seventh entry from the bottom of the component menu).
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The node on the bottom is called an And (eighth entry from the bottom of the component menu).
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Both of these nodes are from the Schematic technology
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(which is listed as "schematics" in the status area).
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<TD><CENTER><IMG SRC="../images/chap01-18.png" ALT="Figure 1.18"></CENTER></TD><TD>
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A <I>highlighted</I> node has two selected parts: the node and a port on that node.
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Note that the And is highlighted in the example above,
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and the Buffer is highlighted in the example here.
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The little "+" sign is the currently highlighted port
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(there are two possible ports on these nodes, on the input and the output).
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To highlight a node, use the <I><A HREF="chap01-08.html#chap01-08" TITLE="UNIX:left Windows:left Mac:click">selection</A></I> button.
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The node, and the closest port to the cursor, will be selected.
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After highlighting, you can hold the mouse button down and drag the highlighted object to a new location.
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If nothing is under the cursor when the selection button is pushed,
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you may drag the cursor while the button remains down to define an area in which all objects will be selected.
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Another way to affect what is highlighted is to use the
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<I><A HREF="chap01-08.html#chap01-08" TITLE="UNIX:shift-left Windows:shift-left Mac:shift-click">toggle select</A></I> button.
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The <I>toggle select</I> button causes object highlighting to be reversed
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(highlighted objects become unhighlighted and unhighlighted objects are highlighted).
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The shape of the highlighted port is important.
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Ports are the sites of arc connections,
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so the end point of the arc must fall inside this port area.
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Ports may be rectangles, lines, single points (displayed as a "+"), or any arbitrary shape.
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For example, the entire left side of the And gate is the input port and so its highlighting is a line.
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To wire a component, select it, move the cursor away from the component,
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and use the <I><A HREF="chap01-08.html#chap01-08" TITLE="UNIX:right Windows:right Mac:cmd-click">creation</A></I> button.
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A wire will be created that runs from the component to the location of the cursor.
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Note that the wire is a fixed-angle wire which means that it will be drawn along a horizontal or vertical path from the originating node.
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To see where the wire will end,
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click but do not release the button and drag the outline of the wire's terminating node
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(a pin) until it is in the proper location.
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It is highly recommended that you do all wiring operations this way, because wiring is quite complex and can follow many different paths.
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</TD><TD><CENTER><IMG SRC="../images/chap01-19.png" ALT="Figure 1.19"></CENTER></TD></TR></TABLE>
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Once a wire has been created, the other end is highlighted (see above).
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This is the highlighting of a <I>pin</I> node that was created to hold the other end of the arc.
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Because it is a node,
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the <I><A HREF="chap01-08.html#chap01-08" TITLE="UNIX:right Windows:right Mac:cmd-click">creation</A></I>
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button can be used again to continue the wire to a new location.
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If the creation command terminates over an existing component,
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the wire will attach to that component.
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One aspect of the And, Or, and Xor gates that you will notice is that their left side
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(the input side) can accept any number of wires.
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To see this in action, place one of these components in the facet.
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Then repeatedly select its left side and use the
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<I><A HREF="chap01-08.html#chap01-08" TITLE="UNIX:right Windows:right Mac:cmd-click">creation</A></I> button to draw wires out of it.
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After three wires have been connected to the input side,
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the gate grows to accommodate more.
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Note that the vertical cursor location along the input side is used to select the position that will be used when a new wire is added.
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<CENTER><IMG SRC="../images/chap01-14.png" ALT="Figure 1.14"></CENTER>
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To negate an input or output of a digital gate,
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you must negate the wire connected to that gate.
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Select a wire and use the <B>Negated</B> command from the <B>Arc</B> menu.
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With this facility, you can construct arbitrary gate configurations.
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</TD><TD><CENTER><IMG SRC="../images/chap01-15.png" ALT="Figure 1.15"></CENTER></TD></TR></TABLE>
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To remove wires or components,
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you can issue the <B>Undo</B> command of the <B>Edit</B> menu to remove the last created object.
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Alternatively, you can select the component and use the <B>Erase</B> command from the <B>Edit</B> menu.
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Once components are wired, moving them will also move their connecting wires.
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Notice that the wires stretch and move to maintain the connections.
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What actually happens is that the programmable constraint system follows instructions stored on the
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wires, and reacts to component changes.
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The default wire is <I>fixed-angle</I> and <I>slidable</I>,
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so the letters "FS" are shown when the wire is highlighted.
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Select a wire and issue the <B>Rigid</B> command of the <B>Arc</B> menu.
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The letters change to "R" on the arc and the wire no longer stretches when components move.
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Find another arc and issue the <B>Not Fixed-angle</B> command in the <B>Arc</B> menu.
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Now observe the effects of an unconstrained arc as its neighboring nodes move.
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These arc constraints can be reversed with the <B>Rigid</B> and <B>Fixed-angle</B> commands.
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Electric supports hierarchy by allowing you to create icons for a schematic and place them in another facet.
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Before creating an icon, all connection points to the schematic should be defined.
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<TD><CENTER><IMG SRC="../images/chap01-22.png" ALT="Figure 1.22"></CENTER></TD><TD>
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Before creating an icon, there must be connection sites, or <I>exports</I> on the schematic.
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Select the output port of the Buffer node and issue the <B>Create Export...</B> command from the <B>Export</B> menu.
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You will be prompted for an export name and its characteristics
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(the characteristics can be ignored for now).
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<TD><CENTER><IMG SRC="../images/chap01-20.png" ALT="Figure 1.20"></CENTER></TD><TD>
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The output port on the buffer node is now exported to the outside world.
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Run a wire from the input side of the And node and export the pin at the end of the wire.
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Your circuit should look like this.
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You can now make an icon for this circuit by using the <B>Make Icon</B> command of the <B>View</B> menu.
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The icon will be placed in your circuit (you may have to move it away from the rest of the circuitry).
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The result will look like this.
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</TD><TD><CENTER><IMG SRC="../images/chap01-21.png" ALT="Figure 1.21"></CENTER></TD></TR></TABLE>
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Now create a new facet with the <B>Edit Facet...</B> command of the <B>Facets</B> menu.
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Click on the "New Facet" button at the bottom,
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and make sure the "Make new window for facet" option is checked in the dialog.
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Then type the new facet name ("Higher" is used in the example here) and set its view.
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</TD><TD><CENTER><IMG SRC="../images/chap01-25.png" ALT="Figure 1.25"></CENTER></TD></TR></TABLE>
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A new (empty) facet will appear in a separate window.
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Try creating a few simple nodes in this new window (place a gate or two).
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<TD><CENTER><IMG SRC="../images/chap01-10.png" ALT="Figure 1.9"></CENTER></TD><TD>
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Now place an instance of the other facet by using the <B>New Facet Instance...</B> command from the <B>Edit</B> menu.
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You will be given a list of facets to create:
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select the one that is in the OTHER window (the one called "MyCircuit{ic}" in this example).
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Then click in the newer facet to create the instance.
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The icon that appears is a node in the same sense as the Buffer and And gate:
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it can be moved, wired, and so on.
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In addition, because the node contains subcomponents,
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you can see its contents by selecting it and using the
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<B>Down Hierarchy</B> command in the <B>Facets</B> menu.
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Note that if the objects in a facet no longer fit in the display window,
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use the <B>Fill Window</B> command from the <B>Windows</B> menu.
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</TD><TD><CENTER><IMG SRC="../images/chap01-23.png" ALT="Figure 1.23"></CENTER></TD></TR></TABLE>
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Some final commands that should be mentioned in this introductory example are the <B>Save Library</B>
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and the <B>Quit</B> commands which can be found in the <B>File</B> menu.
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They do the obvious things.
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Also, the <B>Help...</B> command from the <B>Info</B> menu is very useful.
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It displays a dialog with a list of subjects and offers information about each one.
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