Re: problem with busses

[Steven Rubin]

> Hello. I'm new to VLSI designing, and I'm trying to learn with Electric. I
> just installed 6.03 with lesstif-0.92.29. I'm doing mainly digital
> schematics for now.
>
> The main problem right now is that I can't seem to be able to create ports
> with output pin with three states: on, off and floating. The component
> that should do that is "transmission gate" but I couldn't find one from
> the component menu.

Electric does have transmission gates, one of the "4-port" symbols in the 
Analog Schematics technology.

> I tried to built one from transistors (looking a model from a book), in
> analog schematics, but it didn't seem to work.
>
> One idea would be to use MUX and add two input wires to it (besides
> control line), of which another is input data and another is floating.
> Unfortunately, I can not use it because the simulator says:
>         "ERROR: Model 'MUX2' not found, simulation aborted"
> Can't muxes be used if simulation is wanted?

The simulator doesn't have models for all of the analog schematic symbols.

> First I thought that the third pin in a buffer/inverter would do that but
> it doesn't seem to do anything at all. What it is used for?

Many of the drawing parts in the schematics technology are just that: 
graphic facilities.  It is up to the various tools to make use of 
them.  Thus, a terminal may be understood and used by an output deck 
generator, but not by some other simulation interface.  The built-in 
simulator is not complete in this regard, either.

> I create a new facet. I insert a bus pin and create a bus by dragging from
> the pin. I click the other end and Create Export "a[0:1]". Then I click
> the other end and Create Export "b[0:1]". These are clearly connected,
> right? When I double click on the bus, it shows Bus size 2, which is
> correct.
>
> The problem is that when I use simulator and set some values in the
> another Export, the other one doesn't change. That is, I can not get
> busses to work with simulator at all. What did I do wrong?

You have indeed uncovered a bug.  The conversion of busses to VHDL is 
flawed.  I will look into it.

> Also, is this list dead? I've been subscribed here for couple of days but
> received no mails.

Not dead, just no critical mass yet.  A few of us read it.

   -Steven Rubin