[Magic-dev] Re: "extra" nodes from magic extract

[Piyush Sood]

Tim,

Thanks very much for your detailed reply. It all makes perfect sense
now. I was under the impression that these nodes might somehow be
interfering with the simulation and implementation of my
designs/layouts. After completing the layout and running the
simulation, I realized that in fact they don't.

Thanks again,
Piyush.

On 4/15/05, R. Timothy Edwards <tim at opencircuitdesign.com> wrote:
> Dear Piyush,
> 
> > So my question is that where do these nodes "a_n36_n9#" and
> > "a_n1_n3#" etc come from?
> 
> Magic's names for unlabeled nodes can be interpreted as:
> 
>         (plane_short_name)_(x_position)_(y_position)#
> 
> where the 'plane short name' is found in scmos.tech but generally
> follows the convention w=well, a=active, m1=metal1, etc., and "n"
> in front of a number means negative.
> 
> So you can track down the node "a_n36_n9#" by looking for the
> layer on active (diffusion or poly) at position (-36, -9).
> 
> There really are 12 nodes in your layout.  In addition to the
> labeled nodes, two transistors have unconnected ends (which were
> presumably intended to attach to "test", perhaps by the misplaced
> piece of metal1, which gets counted as another node).  There is
> also one internal node in the AND gate between the two nMOS
> transistors, and then there are the two wells which will be
> considered isolated until connected to vdd with a "nsc" contact.
> 
> It is not necessary to have drawn wells for an extraction, but it
> is necessary to have the well and substrate contacts in a circuit
> if you want it to work correctly.  If you put both nwell and pwell
> and connect both with contacts, you will get the proper substrate
> (bulk) contacts to the transistor devices in the netlist.  If you
> leave the wells undrawn, you will get the default nodes "Vdd!" and
> "Gnd!" in those positions, which must be equated somehow with
> the power and ground networks.  In magic-7.1, you would need to
> label your power and ground networks "Vdd!" and "Gnd!", resepectively.
> In the Tcl/Tk versions of magic-7.2 and 7.3, you can just put the
> Tcl commands "set VDD vdd" and "set GND gnd" to denote that your default
> well and substrate nodes are connected to those nets (which is,
> of course, a misleading idealization if you don't have the well
> and substrate ties).
> 
>                                         Regards,
>                                         Tim
>