docs/wiki/geda-na_howto.html

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  13 <p>
  14 <em>Translations of this page are also available in the following languages:</em> <a href="geda-na_howto.ru.html" class="wikilink1" title="geda-na_howto.ru.html">Русский</a>.
  15 </p>
  16
  17 <h1 class="sectionedit1" id="net_attribute_mini-howto">net= attribute mini-HOWTO</h1>
  18 <div class="level1">
  19
  20 <p>
  21 by: Ales Hvezda
  22 </p>
  23
  24 <p>
  25 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>
  26 </p>
  27
  28 <p>
  29 October 2nd, 2003
  30 </p>
  31
  32 <p>
  33 The information in this document is current as of 19991011.
  34 </p>
  35
  36 </div>
  37 <!-- EDIT1 SECTION "net= attribute mini-HOWTO" [111-326] -->
  38 <h2 class="sectionedit2" id="what_is_the_net_attribute_used_for">What is the net= attribute used for?</h2>
  39 <div class="level2">
  40
  41 <p>
  42 The <strong><code>net=</code></strong> attribute is used to specify power, ground, and/or arbitrary nets in the gEDA system.<br/>
  43
  44 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.
  45 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.
  46 </p>
  47
  48 </div>
  49 <!-- EDIT2 SECTION "What is the net= attribute used for?" [327-1132] -->
  50 <h2 class="sectionedit3" id="what_is_the_format_of_the_net_attribute">What is the format of the net= attribute?</h2>
  51 <div class="level2">
  52
  53 <p>
  54 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/>
  55
  56 Attribute can be attached to an object or in certain cases (like the <strong><code>net=</code></strong> attribute) can be free floating (not attached to anything). The free floating attributes
  57 are also called toplevel attributes.<br/>
  58
  59 The <strong><code>net=</code></strong> attribute is a text item which takes on the following form:
  60 </p>
  61 <pre class="code">net=signalname:pinname,pinname,pinname,...</pre>
  62
  63 <p>
  64 where:
  65 </p>
  66 <div class="table sectionedit4"><table class="inline">
  67         <tr class="row0">
  68                 <td class="col0"> <strong><code>net=</code></strong> </td><td class="col1"> The attribute name (always the same, lowercase) </td>
  69         </tr>
  70         <tr class="row1">
  71                 <td class="col0"> signalname </td><td class="col1"> The signal or net being defines (like +5V, GND, etc…) </td>
  72         </tr>
  73         <tr class="row2">
  74                 <td class="col0"> pinname </td><td class="col1"> The pin name (or number) which is assigned to this signal/net (or pin names/numbers) </td>
  75         </tr>
  76 </table></div>
  77 <!-- EDIT4 TABLE [1835-2073] -->
  78 <p>
  79 The signalname cannot contain the “:” character (since it is a delimiter). The pinname is the pin name (A1, P2, D1, etc…) or pin number (1, 2, 5, 13, etc…). The pinname cannot contain the “,” 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/>
  80
  81 You can only have ONE signalname per <strong><code>net=</code></strong> attribute, but you can have as many pinnames/numbers as you want.
  82 </p>
  83
  84 </div>
  85 <!-- EDIT3 SECTION "What is the format of the net= attribute?" [1133-2558] -->
  86 <h2 class="sectionedit5" id="how_do_you_actually_use_the_net_attribute">How do you actually use the net= attribute?</h2>
  87 <div class="level2">
  88
  89 <p>
  90 You can place the <strong><code>net=</code></strong> attribute in several places. Here&#039;s the list so far:
  91 </p>
  92 <ul>
  93 <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>
  94 </li>
  95 <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>
  96 </li>
  97 <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>
  98 </li>
  99 <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/>
 100 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… 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/>
 101 There also symbols named 5V-minus-1.sym, 12V-plus-1.sym, 9V-plus-1.sym, etc… 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/>
 102 </div>
 103 </li>
 104 </ul>
 105
 106 <p>
 107 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&#039;t work, please <a href="geda-howto_report_bugs.html" class="wikilink1" title="geda-howto_report_bugs.html">report a bug</a>.
 108 </p>
 109
 110 </div>
 111 <!-- EDIT5 SECTION "How do you actually use the net= attribute?" [2559-4453] -->
 112 <h2 class="sectionedit6" id="caveats_bugs">Caveats / Bugs</h2>
 113 <div class="level2">
 114
 115 <p>
 116 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:
 117 </p>
 118 <ul>
 119 <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>
 120 </li>
 121 <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>
 122 </li>
 123 <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>
 124 </li>
 125 <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>
 126 </li>
 127 </ul>
 128
 129 </div>
 130 <!-- EDIT6 SECTION "Caveats / Bugs" [4454-5665] -->
 131 <h2 class="sectionedit7" id="example">Example</h2>
 132 <div class="level2">
 133
 134 <p>
 135 Here&#039;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/>
 136
 137 </p>
 138 <div class="table sectionedit8"><table class="inline">
 139         <tr class="row0">
 140                 <td class="col0"> <a href="media/geda/net.jpg" class="media" target="_blank" title="geda:net.jpg"><img src="media/geda/net.jpg" class="media" alt="" /></a> </td>
 141         </tr>
 142 </table></div>
 143 <!-- EDIT8 TABLE [6286-6307] --><pre class="code">v 19991011
 144 C 38700 58100 1 0 0 7400-1.sym
 145 {
 146 T 39000 59000 5 10 1 1 0
 147 uref=U100
 148 T 38900 59500 5 10 1 1 0
 149 net=GND:7
 150 T 38900 59300 5 10 1 1 0
 151 net=+5V:14
 152 }
 153 N 38700 58800 37400 58800 4
 154 {
 155 T 37600 58900 5 10 1 1 0
 156 netname=NETLABEL
 157 }
 158 N 37400 58800 37400 59200 4
 159 N 38700 58400 37400 58400 4
 160 N 37400 58000 37400 58400 4
 161 C 37300 57700 1 0 0 gnd-1.sym
 162 C 37200 59200 1 0 0 vcc-1.sym
 163 {
 164 T 36800 59200 5 10 1 1 0
 165 net=+5V:1
 166 }
 167 N 40000 58600 41600 58600 4
 168 {
 169 T 41200 58700 5 10 1 1 0
 170 netname=OUTPUT
 171 }
 172 C 40700 58800 1 90 0 resistor-1.sym
 173 {
 174 T 40800 59200 5 10 1 1 0
 175 uref=R1
 176 }
 177 N 40600 58800 40600 58600 4
 178 N 40600 59900 40600 59700 4
 179 C 40400 59900 1 0 0 5V-plus-1.sym</pre>
 180
 181 <p>
 182 <strong>gnetlist</strong> (using the geda netlist format) run using this sample schematic outputs this:
 183 </p>
 184 <pre class="code">START header
 185
 186 gEDA&#039;s netlist format
 187 Created specifically for testing of gnetlist
 188
 189 END header
 190
 191 START components
 192
 193 R1 device=RESISTOR
 194 U100 device=7400
 195
 196 END components
 197
 198 START renamed-nets
 199
 200 NETLABEL -&gt; +5V
 201
 202 END renamed-nets
 203
 204 START nets
 205
 206 +5V : R1 2, U100 14, U100 1
 207 GND : U100 7, U100 2
 208 OUTPUT : R1 1, U100 3
 209
 210 END nets</pre>
 211
 212 <p>
 213 Notice how NETLABEL was renamed (aliased to the +5V net).
 214 </p>
 215
 216 </div>
 217 <!-- EDIT7 SECTION "Example" [5666-7443] -->
 218 <h2 class="sectionedit9" id="final_notes">Final notes</h2>
 219 <div class="level2">
 220
 221 <p>
 222 If you found a bug, please <a href="geda-howto_report_bugs.html" class="wikilink1" title="geda-howto_report_bugs.html">let us know</a>.
 223 </p>
 224
 225 </div>
 226 <!-- EDIT9 SECTION "Final notes" [7444-] --></body>
 227 </html>