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  26 <div class="tocheader toctoggle" id="toc__header">Table of Contents</div>
  27 <div id="toc__inside">
  28
  29 <ul class="toc">
  30 <li class="level1"><div class="li"><span class="li"><a href="#net_attribute_mini-howto" class="toc">net= attribute mini-HOWTO</a></span></div>
  31 <ul class="toc">
  32 <li class="level2"><div class="li"><span class="li"><a href="#what_is_the_net_attribute_used_for" class="toc">What is the net= attribute used for?</a></span></div></li>
  33 <li class="level2"><div class="li"><span class="li"><a href="#what_is_the_format_of_the_net_attribute" class="toc">What is the format of the net= attribute?</a></span></div></li>
  34 <li class="level2"><div class="li"><span class="li"><a href="#how_do_you_actually_use_the_net_attribute" class="toc">How do you actually use the net= attribute?</a></span></div></li>
  35 <li class="level2"><div class="li"><span class="li"><a href="#caveats_bugs" class="toc">Caveats / Bugs</a></span></div></li>
  36 <li class="level2"><div class="li"><span class="li"><a href="#example" class="toc">Example</a></span></div></li>
  37 <li class="level2"><div class="li"><span class="li"><a href="#final_notes" class="toc">Final notes</a></span></div></li></ul>
  38 </li></ul>
  39 </div>
  40 </div>
  41
  42
  43
  44 <h1><a name="net_attribute_mini-howto" id="net_attribute_mini-howto">net= attribute mini-HOWTO</a></h1>
  45 <div class="level1">
  46
  47 <p>
  48 by: Ales Hvezda
  49 </p>
  50
  51 <p>
  52 This document is released under <a href="http://www.gnu.org/copyleft/fdl.html" class="urlextern" title="http://www.gnu.org/copyleft/fdl.html"  rel="nofollow">GFDL</a>
  53 </p>
  54
  55 <p>
  56 October 2nd, 2003
  57 </p>
  58
  59 <p>
  60 The information in this document is current as of 19991011.
  61 </p>
  62
  63 </div>
  64 <!-- SECTION "net= attribute mini-HOWTO" [1-216] -->
  65 <h2><a name="what_is_the_net_attribute_used_for" id="what_is_the_net_attribute_used_for">What is the net= attribute used for?</a></h2>
  66 <div class="level2">
  67
  68 <p>
  69 The <strong><code>net=</code></strong> attribute is used to specify power, ground, and/or arbitrary nets in the gEDA system.<br/>
  70  The <strong><code>net=</code></strong> attribute is used instead some of the other systems of specifying power/ground (such as having power/ground pins on symbols or power boxes). Some devices have lots of power/ground pins and having all of these pins on the symbol would increase its size and make it unmanageable. The <strong><code>net=</code></strong> attribute is the power/ground specification of choice in the gEDA system because of its simplicity and versatility. Now having said all this, you can have power/ground pins on a symbol, but gnetlist will probably not recognize these nets connected to these pins as separate power/ground nets. Please keep this in mind as you draw symbols.
  71 </p>
  72
  73 </div>
  74 <!-- SECTION "What is the net= attribute used for?" [217-1022] -->
  75 <h2><a name="what_is_the_format_of_the_net_attribute" id="what_is_the_format_of_the_net_attribute">What is the format of the net= attribute?</a></h2>
  76 <div class="level2">
  77
  78 <p>
  79 Attributes in gEDA are simple text items which are in the form <code>name=value</code>. All proper attributes follow this form. Attribute names are always lower case, but the value can be upper or lower case. gnetlist and friends are case sensitive. Typically net/signal names by default are upper case.<br/>
  80  Attribute can be attached to an object or in certain cases (like the <strong><code>net=</code></strong> attribute) can be free oating (not attached to anything). The free floating attributes are also called toplevel attributes.<br/>
  81  The <strong><code>net=</code></strong> attribute is a text item which takes on the following form:
  82 </p>
  83 <pre class="code">net=signalname:pinname,pinname,pinname,...</pre>
  84
  85 <p>
  86 where:
  87 </p>
  88 <table class="inline">
  89         <tr>
  90                 <td> <strong><code>net=</code></strong> </td><td> The attribute name (always the same, lowercase) </td>
  91         </tr>
  92         <tr>
  93                 <td> signalname </td><td> The signal or net being defines (like +5V, GND, etc&hellip;) </td>
  94         </tr>
  95         <tr>
  96                 <td> pinname </td><td> The pin name (or number) which is assigned to this signal/net (or pin names/numbers) </td>
  97         </tr>
  98 </table>
  99
 100 <p>
 101  The signalname cannot contain the &quot;:&quot; character (since it is a delimiter). The pinname is the pin name (A1, P2, D1, etc&hellip;) or pin number (1, 2, 5, 13, etc&hellip;). The pinname cannot contain the &quot;,&quot; character (since it is also a delimiter). pinnames are typically the same sort of numbers/names like the <code>pin#=#</code> attribute (if you are familiar with that attribute).<br/>
 102  You can only have ONE signalname per <strong><code>net=</code></strong> attribute, but you can have as many pinnames/numbers as you want.
 103 </p>
 104
 105 </div>
 106 <!-- SECTION "What is the format of the net= attribute?" [1023-2446] -->
 107 <h2><a name="how_do_you_actually_use_the_net_attribute" id="how_do_you_actually_use_the_net_attribute">How do you actually use the net= attribute?</a></h2>
 108 <div class="level2">
 109
 110 <p>
 111 You can place the <strong><code>net=</code></strong> attribute in several places. Here’s the list so far:
 112 </p>
 113 <ul>
 114 <li class="level1"><div class="li"> Inside a symbol either as an attached attribute or an unattached attribute (toplevel attribute). Example which creates power/gnd nets: <strong><code>net=GND:7</code></strong> or <strong><code>net=+5V:14</code></strong></div>
 115 </li>
 116 <li class="level1"><div class="li"> Outside a symbol (which is instantiated on a schematic) attached as an attribute to override an existing <strong><code>net=</code></strong> created net/signal. Suppose a symbol has a <strong><code>net=GND:7</code></strong> inside it already; attaching this to the symbol: <strong><code>net=AGND:7</code></strong> overrides the GND net (on pin 7) calling it AGND and connects/associates it to pin 7.</div>
 117 </li>
 118 <li class="level1"><div class="li"> Outside or inside a symbol to connect a net to a visible pin automatically. This is still untested and still might have some undesirable (negative) side effects. Use with caution.</div>
 119 </li>
 120 <li class="level1"><div class="li"> Attached to one of those special power/gnd symbol (like vcc/gnd/vdd) and you can change what that symbol represents. You could change the ground symbol to create a net called DIGITAL GND without editing the symbol (<strong><code>net=DIGITAL_GND:1</code></strong>).<br/>
 121  In the current symbol (19991011) library there are symbols named <strong>vdd-1.sym</strong>, <strong>vcc-1.sym</strong>, <strong>vee-1.sym</strong>, etc&hellip; which do not have a <strong><code>net=</code></strong> attribute inside, so you must attach the <strong><code>net=</code></strong> attribute yourself (in the schematic).<br/>
 122  There also symbols named 5V-minus-1.sym, 12V-plus-1.sym, 9V-plus-1.sym, etc&hellip; which have the appropriate <strong><code>net=</code></strong> attribute in them already (can be overridden though). You can use these symbol as examples of how to use the <strong><code>net=</code></strong> attribute.<br/>
 123 </div>
 124 </li>
 125 </ul>
 126
 127 <p>
 128 You can have as many <strong><code>net=</code></strong> attributes as you want. Just remember that <strong><code>net=</code></strong> attributes attached to the outside of a symbol override any equivalent internal (inside the symbol) <strong><code>net=</code></strong> attributes. If you run into a case where this doesn’t work, please let <strong>ahvezdaATgeda.seul.org</strong>. In fact, send any bug reports to that individual.
 129 </p>
 130
 131 </div>
 132 <!-- SECTION "How do you actually use the net= attribute?" [2447-4387] -->
 133 <h2><a name="caveats_bugs" id="caveats_bugs">Caveats / Bugs</a></h2>
 134 <div class="level2">
 135
 136 <p>
 137 The <strong><code>net=</code></strong> attribute/mechanism is fairly new, so there are bound to be bugs (many bugs). Here are some of the identified issues:
 138 </p>
 139 <ul>
 140 <li class="level1"><div class="li"> As of 19991011 almost all of the symbols in the standard library do not have the <strong><code>net=</code></strong> attribute or any other power/ground specifiers. Hopefully this will be updated sometime (any volunteers?).</div>
 141 </li>
 142 <li class="level1"><div class="li"> Attach a special power symbol (vcc/gnd) to a already named net will alias (rename) that net to the signalname specified in the <strong><code>net=</code></strong> attribute (in/attached to the vcc/gnd symbol). You can override this (so the reverse is true) by playing with the “net-naming-priority”. Be careful with this. There might be other “aliasing” issues which have not been identified yet.</div>
 143 </li>
 144 <li class="level1"><div class="li"> Creating a <strong><code>net=</code></strong> attribute which associates a signal name with a pin which is already visible on the symbol, is probably a bad idea. This does work, but all the ramifications have not been explored yet.</div>
 145 </li>
 146 <li class="level1"><div class="li"> It is probably a bad idea to have the same <strong><code>net=</code></strong> attribute attached several times. Ales has not formalized what happens in this case. Just remember that the <strong><code>net=</code></strong> attribute on the outside of a symbol should override the internal one.</div>
 147 </li>
 148 </ul>
 149
 150 </div>
 151 <!-- SECTION "Caveats / Bugs" [4388-5599] -->
 152 <h2><a name="example" id="example">Example</a></h2>
 153 <div class="level2">
 154
 155 <p>
 156 Here’s a schematic which uses standard symbols (note: the 7400 does not have the <strong><code>net=</code></strong> attribute inside yet). This schematic consists of a 7400 with the <strong><code>net=</code></strong> attributes attached for power and ground, One of the input pins grounded using a gnd symbol and the other at a logic one using the vcc symbol (with an attached <strong><code>net=</code></strong> attribute). One of the input net is named, but as you will see, the netname is replaced by the <strong><code>net=</code></strong> signal name (see above for more info on this). The output is pulled up with a pull up resistor which has power specified using the +5V symbol.<br/>
 157
 158 </p>
 159 <table class="inline">
 160         <tr>
 161                 <td> <a href="_detail/geda_net.html" class="media" title="geda:net.jpg"><img src="_media/geda_net.jpg" class="media" title="net.jpg" alt="net.jpg" /></a> </td>
 162         </tr>
 163 </table>
 164 <pre class="code">v 19991011
 165 C 38700 58100 1 0 0 7400-1.sym
 166 {
 167 T 39000 59000 5 10 1 1 0
 168 uref=U100
 169 T 38900 59500 5 10 1 1 0
 170 net=GND:7
 171 T 38900 59300 5 10 1 1 0
 172 net=+5V:14
 173 }
 174 N 38700 58800 37400 58800 4
 175 {
 176 T 37600 58900 5 10 1 1 0
 177 netname=NETLABEL
 178 }
 179 N 37400 58800 37400 59200 4
 180 N 38700 58400 37400 58400 4
 181 N 37400 58000 37400 58400 4
 182 C 37300 57700 1 0 0 gnd-1.sym
 183 C 37200 59200 1 0 0 vcc-1.sym
 184 {
 185 T 36800 59200 5 10 1 1 0
 186 net=+5V:1
 187 }
 188 N 40000 58600 41600 58600 4
 189 {
 190 T 41200 58700 5 10 1 1 0
 191 netname=OUTPUT
 192 }
 193 C 40700 58800 1 90 0 resistor-1.sym
 194 {
 195 T 40800 59200 5 10 1 1 0
 196 uref=R1
 197 }
 198 N 40600 58800 40600 58600 4
 199 N 40600 59900 40600 59700 4
 200 C 40400 59900 1 0 0 5V-plus-1.sym</pre>
 201
 202 <p>
 203 <strong>gnetlist</strong> (using the geda netlist format) run using this sample schematic outputs this:
 204 </p>
 205 <pre class="code">START header
 206
 207 gEDA&#039;s netlist format
 208 Created specifically for testing of gnetlist
 209
 210 END header
 211
 212 START components
 213
 214 R1 device=RESISTOR
 215 U100 device=7400
 216
 217 END components
 218
 219 START renamed-nets
 220
 221 NETLABEL -&gt; +5V
 222
 223 END renamed-nets
 224
 225 START nets
 226
 227 +5V : R1 2, U100 14, U100 1
 228 GND : U100 7, U100 2
 229 OUTPUT : R1 1, U100 3
 230
 231 END nets</pre>
 232
 233 <p>
 234 Notice how NETLABEL was renamed (aliased to the +5V net).
 235 </p>
 236
 237 </div>
 238 <!-- SECTION "Example" [5600-7377] -->
 239 <h2><a name="final_notes" id="final_notes">Final notes</a></h2>
 240 <div class="level2">
 241
 242 <p>
 243 Send all bugs to <strong>ahvezdaATgeda.seul.org</strong> or <strong>geda-devATgeda.seul.org</strong> (mailing list, please subscribe first). [I’m sure there’s more to say here]
 244 </p>
 245
 246 </div>
 247 <!-- SECTION "Final notes" [7378-] --></div>
 248 </body>
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