[Xcircuit-dev] xcircuit netlist -> pcb

[Bryce D. <br...@tl...>]

Between xcircuit and pcb, we are really close to having a schematic+layout
flow for circuit boards.  With some hacking, I've been able to make it
work for a sample schematic.

Pcb's netlist reader is very picky about pin numbers and node names.  It
refers to all pins by number, and ignores lowercase letters in some
circumstances.  All the transistor models in generic and analoglib2 have
letter-named pins, such as B for base and E for emitter, so I had to
rename these pins to 1,2,3 to make the netlist valid.  You might want the
pcb netlister to print a warning about letter-named pins, since pcb itself
will choke when it tries to read them in.  This is really a pcb limitation
(I can't believe they can't handle pin names) but that's how it is at the
moment.

For reference, here's what the pcb manual says about the netlist format
that it expects.

  "The netlist received by pcb must have this simple text form: netname
NAME-PINNUM NAME2-PINNUM2 NAME3-PINNUM3 ... [\] where "netname" is the
name of the net (currently its value is ignored but it must be present
nonetheless), NAME is the layout-name given to an element, and PINNUM is
the (usually numeric) pin number of the element that is part of the net
(see section Elements for details on pin numbering). Spaces or tabs
separate the fields. If the line ends with a "\" the net continues on the
next line and the "\" is treated exactly as if it were a space. If the
NAME ends with a lower-case letter, all lower-case letters are stripped
from end of the NAME to determine the matching name-on-board name. For
example: Data U1-3 U2abc-4 FLOP1a-7 Uabc3-A9 would specifiy that pin 3 of
U1 be connected to pin 4 of U2, to pin 7 of FLOP1 and to pin A9 of Uabc3."

Another issue that's minor but confusing is that it's possible to get two
Vdd nodes in the netlist.  Draw a Vdd symbol and also name a pin Vdd in
the diagram.  If you forget to connect them, the netlist writer prints one
Vdd from the "Vdd module" and a different one for the pin called Vdd.

Thanks,
Bryce