192 lines
6.9 KiB
HTML
192 lines
6.9 KiB
HTML
<!DOCTYPE html>
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<html>
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<head>
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<title>XSCHEM TUTORIAL: SYMBOL AND SCHEMATIC GENERATORS</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="xschem_man.html" class="home">UP</a>
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<!-- slide title -->
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<h1> TUTORIAL: SYMBOL AND SCHEMATIC GENERATORS (aka PCELLS)</h1>
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<p>
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It is possible to insert a symbol by referencing a generator script instead of a <kbd>.sym</kbd> file.
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When inserting the symbol select the <kbd>All</kbd> checkbox to see all files , select the generator script,
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then in the File/Search textbox add two parenthesis <kbd>()</kbd> (or put required parameters in
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between, like <kbd>(buf,250)</kbd>). If you don't append the <kbd>()</kbd> xschem will do that for you.
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</p>
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<img src="symbol_generators01.png">
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<p>
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The symbolgen.tcl generator in this example takes two parameters, a <kbd>(buf)</kbd> or a <kbd>(inv)</kbd>
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parameter to generate a buffer or an inverter, respectively, and a output resistance value (a number)
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If no parameters are given (empty parentheses) a buffer is generated with a default ROUT.
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<br>
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</p>
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<img src="symbol_generators04.png">
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<p>
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In this example a tcl script is used, you can use any language you like. The script only needs to parse
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the parameters (if any) and outputs on standard output a regular xschem symbol file.
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</p>
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<pre class="code">
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#!/bin/sh
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# the next line restarts using wish \
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exec tclsh "$0" "$@"
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set arg1 [lindex $argv 0]
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set rout [lindex $argv 1]
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# puts stderr "arg1=|$arg1| $rout=|$rout|"
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if { $arg1 eq {inv}} {
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puts "v {xschem version=3.1.0 file_version=1.2}
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K {type=subcircuit
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xvhdl_primitive=true
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xverilog_primitive=true
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xvhdl_format=\"@@y <= not @@a after 90 ps;\"
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xverilog_format=\"assign #90 @@y = ~@@a ;\"
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format=\"@name @pinlist @symname wn=@wn lln=@lln wp=@wp lp=@lp\"
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template=\"name=x1 wn=1u lln=2u wp=4u lp=2u\"
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schematic=schematicgen.tcl(inv)}
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L 4 -40 0 -20 0 {}
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L 4 -20 -20 20 0 {}
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L 4 -20 -20 -20 20 {}
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L 4 -20 20 20 0 {}
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L 4 30 -0 40 -0 {}
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B 5 37.5 -2.5 42.5 2.5 {name=y dir=out }
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B 5 -42.5 -2.5 -37.5 2.5 {name=a dir=in }
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A 4 25 -0 5 180 360 {}
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T {$arg1 $rout} -47.5 24 0 0 0.3 0.3 {}
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T {@name} 25 -22 0 0 0.2 0.2 {}
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T {y} 7.5 -6.5 0 1 0.2 0.2 {}
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T {a} -17.5 -6.5 0 0 0.2 0.2 {}
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"
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} else {
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puts "v {xschem version=3.1.0 file_version=1.2}
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K {type=subcircuit
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xvhdl_primitive=true
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xverilog_primitive=true
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xvhdl_format=\"@@y <= @@a after 90 ps;\"
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xverilog_format=\"assign #90 @@y = @@a ;\"
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format=\"@name @pinlist @symname wn=@wn lln=@lln wp=@wp lp=@lp\"
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template=\"name=x1 wn=1u lln=2u wp=4u lp=2u\"
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schematic=schematicgen.tcl(buf)}
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L 4 20 0 40 0 {}
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L 4 -40 0 -20 0 {}
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L 4 -20 -20 20 0 {}
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L 4 -20 -20 -20 20 {}
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L 4 -20 20 20 0 {}
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B 5 37.5 -2.5 42.5 2.5 {name=y dir=out }
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B 5 -42.5 -2.5 -37.5 2.5 {name=a dir=in }
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T {$arg1 $rout} -47.5 24 0 0 0.3 0.3 {}
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T {@name} 25 -22 0 0 0.2 0.2 {}
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T {y} 7.5 -6.5 0 1 0.2 0.2 {}
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T {a} -17.5 -6.5 0 0 0.2 0.2 {}
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"
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}
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</pre>
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<p>
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The <kbd>generators/test_symbolgen.sch</kbd> is a test schematic that places two instances of this
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symbol generator, one as <kbd>symbolgen.tcl(buf,@ROUT\)</kbd> and one as <kbd>symbolgen.tcl(inv,@ROUT\)</kbd>.
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The <kbd>buf,@ROUT</kbd> indicates two parameters, one indicates if it is a buffer or an inverter,
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the second passes an additional parameter. Instead of using a numeric literal the instance
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value ROUT is passed to the generator.
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A backslash is needed before the closing parenthesis to avoid this parenthesis to be considered
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as part of the parameter.
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The schematic implementations of these symbols are defined by the generator using a <kbd>schematic</kbd>
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attribute. The buffer will use <kbd>schematicgen.tcl(buf)</kbd> and the inverter will
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use <kbd>schematicgen.tcl(inv)</kbd>, these schematic names are referencing a schematic generator
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script instead of regular schematic files.
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You see different schematics (see below picture) when descending the buf or inv generator.
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See next section about schematic generators.
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</p>
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<img src="symbol_generators02.png">
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<p>
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The following is the extracted netlist from this example:
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</p>
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<pre class="code">
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** sch_path: /home/schippes/xschem-repo/trunk/xschem_library/generators/test_symbolgen.sch
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**.subckt test_symbolgen
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x1 IN_INV IN symbolgen_tcl_inv_1200 wn=1u lln=2u wp=4u lp=2u
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x3 IN_BUF IN symbolgen_tcl_buf_1200 wn=1u lln=2u wp=4u lp=2u
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C1 IN_BUF 0 100f m=1
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C2 IN_INV 0 100f m=1
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**** begin user architecture code
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.include models_rom8k.txt
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.param vcc=3
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vvcc vcc 0 dc 3
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Vin in 0 pwl 0 0 100n 0 100.1n 3 200n 3 200.1n 0
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.control
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save all
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tran 1n 300n uic
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write test_symbolgen.raw
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.endc
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**** end user architecture code
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**.ends
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* expanding symbol: symbolgen.tcl(inv,1200) # of pins=2
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** sym_path: /home/schippes/xschem-repo/trunk/xschem_library/generators/symbolgen.tcl
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** sch_path: /home/schippes/xschem-repo/trunk/xschem_library/generators/schematicgen.tcl
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.subckt symbolgen_tcl_inv_1200 y a wn=1u lln=2u wp=4u lp=2u
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*.opin y
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*.ipin a
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m2 y a VCC VCC cmosp w=wp l=lp ad='wp *4.6u' as='wp *4.6u' pd='wp *2+9.2u' ps='wp *2+9.2u' m=1
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m1 y a 0 0 cmosn w=wn l=lln ad='wn *4.3u' as='wn *4.3u' pd='wn *2+8.6u' ps='wn *2+8.6u' m=1
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.ends
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* expanding symbol: symbolgen.tcl(buf,1200) # of pins=2
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** sym_path: /home/schippes/xschem-repo/trunk/xschem_library/generators/symbolgen.tcl
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** sch_path: /home/schippes/xschem-repo/trunk/xschem_library/generators/schematicgen.tcl
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.subckt symbolgen_tcl_buf_1200 y a wn=1u lln=2u wp=4u lp=2u
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*.opin y
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*.ipin a
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m2 net1 a VCC VCC cmosp w=wp l=lp ad='wp *4.6u' as='wp *4.6u' pd='wp *2+9.2u' ps='wp *2+9.2u' m=1
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m1 net1 a 0 0 cmosn w=wn l=lln ad='wn *4.3u' as='wn *4.3u' pd='wn *2+8.6u' ps='wn *2+8.6u' m=1
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m3 y net1 VCC VCC cmosp w=wp l=lp ad='wp *4.6u' as='wp *4.6u' pd='wp *2+9.2u' ps='wp *2+9.2u' m=1
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m4 y net1 0 0 cmosn w=wn l=lln ad='wn *4.3u' as='wn *4.3u' pd='wn *2+8.6u' ps='wn *2+8.6u' m=1
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.ends
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.end
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</pre>
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<p>
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This approach allows to create polymorphic symbols. Multiple parameters may be given to the generator script,
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like <kbd>symbolgen.tcl(inv,hv,100)</kbd>. Xschem will call the symbolgen.tcl script with the following command:
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<kbd>symbolgen.tcl inv hv 100</kbd> and take the standard output from the script as the symbol
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file to load and display.
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</p>
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<h2> Schematic generators (pcells)</h2>
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<p>
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The same approach used for symbol generators can be used for schematic generators. If you add a
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<kbd>schematic=schematicgen.tcl(buf,4)</kbd> attribute to an instance
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xschem will look for a script named <kbd>schematicgeni.tcl</kbd> in the search paths and call
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it with the given parameters (that is, execute the command
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<kbd>schematicgen.tcl buf 4</kbd>) and read the produced output as a schematic file.
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</p>
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<img src="symbol_generators03.png">
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<br><br><br>
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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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