146 lines
6.1 KiB
HTML
146 lines
6.1 KiB
HTML
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<!DOCTYPE html>
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<html>
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<head>
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<title>XSCHEM PROPERTIES</title>
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<link rel="stylesheet" type="text/css" href="xschem_man.css" />
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<style type="text/css">
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/* Local styling goes here */
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p{padding: 15px 30px 10px;}
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</style>
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</head>
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<body>
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<!-- start of slide -->
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<div class="content">
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<!-- navigation buttons -->
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<a href="building_xschem_symbol.html" class="prev">PREV</a>
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<a href="xschem_man.html" class="home">UP</a>
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<a href="component_instantiation.html" class="next">NEXT</a>
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<!-- slide title -->
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<h1>XSCHEM PROPERTIES</h1><br>
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<p>
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Properties are text strings that are associated to XSCHEM objects.
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All graphic primitives support properties.
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</p>
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<ul>
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<li>Wires</li>
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<li>Lines</li>
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<li>Polygons</li>
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<li>Rectangles</li>
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<li>Circles/Arcs</li>
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<li>Texts</li>
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<li>Symbol references</li>
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<li>Global attributes</li>
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</ul>
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<p>
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Consider for example the <kbd>res.sym</kbd> symbol
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(you may open it with the <kbd>File->Open</kbd> menu item)
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if you click inside one of the red pins and press the 'edit property'
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bindkey <kbd>'q'</kbd> a dialog box
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shows the property string associated with the selected pin:
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</p>
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<img src="edit_property.png">
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<p>
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The <kbd>name=p dir=inout propagate_to=1 pinnumber=1</kbd> property string tells that the
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selected pin name is <kbd>'p'</kbd>,
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this will be the symbol positive pin name in the produced netlist.
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The property string also defines a <kbd>dir</kbd> attribute with value
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<kbd>inout</kbd>. This tells XSCHEM that electrically this is an input/output pin.
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This is important when producing VHDL/verilog netlists.
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The <kbd>propagate_to=1</kbd> tells XSCHEM that when we select a wire attaced to this pin
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(which is located at index 0 in xschem) the highlight will propagate to the other pin (with index 1).
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To view the xschem index of a pin click and hold the mouse on it, the index will be shown as
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<kbd>n= <number> </kbd> in the bottom status line:
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</p>
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<img src="edit_property2.png">
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<p>
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The <kbd> pinnumber=1</kbd> attribute is used when exporting to pcb software (via the tEDAx netlist)
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and tells to which pin number on the resistor footprint this positive pin is bound.
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The second (bottom) pin property string is <kbd>name=m dir=inout propagate_to=0 pinnumber=2</kbd> and this
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defines the negative pin.
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The text primitives also have properties. For texts the property string may be used
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to specify font and the layer to use for displaying text.
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</p>
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<img src="text_property.png">
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<h3>GLOBAL PROPERTIES</h3>
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<p>
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If you click outside of any displayed graphics in XSCHEM
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the selection set will be cleared.
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Clicking the edit property <kbd>'q'</kbd> key when nothing is
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selected will display the global property string of the
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schematic (.sch) or symbol window (.sym).
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<p class="important">
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There is actually one different global property
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string defined for any available netlisting modes, so if XSCHEM is set to produce SPICE
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netlists the SPICE global property string is displayed.
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</p>
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<p>
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So, in addition to properties associated to graphical objects and
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symbols, we also have properties associated to schematic (.sch) and symbol files (.sym)
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</p>
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<img src="global_property.png">
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<p>
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The <kbd>format</kbd> attribute defines the format of the SPICE netlist.
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The SPICE netlist element line starts with the
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symbol name (in this case a resistor so 'rxxxxx'), the list of pins, the
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resistor value and a multiplicity factor (m).<br>
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<kbd>@pinlist</kbd> will resolve to the parent nets attached to the resistor
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nodes, in the order they appear in the
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symbol (in this example; first node = 'p', second node = 'm').<br>
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We will return on component instantiation later, but for now,
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considering the following picture:
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</p>
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<img src="nets_pins.png">
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<p>
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The <kbd>@name</kbd> will expand to R0, <kbd>@pinlist</kbd> for the <kbd>R0</kbd>
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component will expand to <kbd>POS NEG</kbd>.<br>
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<kbd>@value</kbd> resolves to the resistor value assigned in component instantiation.
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The <kbd>template</kbd> attribute defines default values if component
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instantiation does not define values for them.<br>
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If you want to add a pin to an existing symbol you may copy one
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of these. Select a pin, press the copy <kbd>'c'</kbd>
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bindkey and place a new copy of it somewhere.
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</p>
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<img src="place_pin.png" style="width: 90%;">
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<p>
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After copying the pin you may change its properties, for example you
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will change its property string to
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something like: <kbd> name=body dir=in</kbd> (just as an example).<br>
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Note that pins in symbols are nothing more than rectangles
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drawn with the <kbd>pin</kbd> layer; instead of copying an
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existing one you may create it from scratch, select the pin
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layer from the <kbd>Layers</kbd> menu, point the mouse where
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you want to place the pin, press the <kbd>'r'</kbd> bindkey and drag the mouse
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to the desired pin size. There is no inherent limit or assumption
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on pin sizes, you are allowed to create any rectangular/square sizes.
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After placing the rectangle you must create a property string by selecting it
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and pressing the <kbd>'q'</kbd> bindkey. An empty string is shown in the
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dialog. Add a valid string as explained and you are all done.
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</p>
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<h3> PIN ORDERING</h3>
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<p>
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An important aspect for symbols is the order of the pins
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when producing the netlist. There are some rules in the order
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for example in SPICE netlist syntax; for example a Bipolar transistor
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has 3 pins and should be in a specific order (collector, base, emitter).
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When done placing pins on a newly created symbol you can specify the order
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by selecting the one that must be the first in the netlist
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and hitting the <kbd>'<shift>S'</kbd> bindkey; set the number to zero;
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this will make the selected pin the first one. Next,
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select the second pin and again hit <kbd>'<shift>S'</kbd>,
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set its number to 1 and so on.
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By doing so you have defined a specific pin ordering of the symbol.
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</p>
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<img src="pin_order.png">
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<!-- end of slide -->
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<div class="filler"></div>
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</div>
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<!-- frame footer -->
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<iframe seamless src="xschem_footer.html" class="footer_iframe" >
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</body>
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</html>
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