R: decoder

[Max]

On Tue, 09 Sep 2003 16:52:11 +0200
"Amontec Team, Laurent Gauch" <[email protected]>
wrote:

> Max wrote:
> > I write the following decoder:
> >
> > ce <= "0001" when addr = "0--" else
> > "0010" when addr = "10-" else
> > "0100" when addr = "110" else
> > "1000";
> >
> > it doesn't work.
> >
> > Then I tried this one:
> >
> > ce <= "0001" when addr(2) = '0' else
> > "0010" when addr(2 downto 1) = "10" else
> > "0100" when addr = "110" else
> > "1000";
> >
> > this work.
> >
> > why the first version doesn't work?
> > the symbol '-' means "don't care", isn't it? So why it is wrong?
> > I prefer something like the first version since is less cryptic.
> >
> > thanks
> I am interested by this issue. Which compiler are you using?
I use Xilinx Web Pack 5.2.
both versions compile fine without errors or warning but when I run the
first model in ModelSim 5.6 I don't obtain what I'm expecting: ce is
always "1000" except when addr is "110".


thanks

[Egbert Molenkamp]

I already explained it in more detail. But ModelSim has the
switch -explicit.
try
vcom -explicit <filename>

and I guess the behavior is as you expect.

Egbert Molenkamp

"Max" <[email protected]> schreef in bericht
news:[email protected] om...
> On Tue, 09 Sep 2003 16:52:11 +0200
> "Amontec Team, Laurent Gauch" <[email protected]>
> wrote:
>
> > Max wrote:
> > > I write the following decoder:
> > >
> > > ce <= "0001" when addr = "0--" else
> > > "0010" when addr = "10-" else
> > > "0100" when addr = "110" else
> > > "1000";
> > >
> > > it doesn't work.
> > >
> > > Then I tried this one:
> > >
> > > ce <= "0001" when addr(2) = '0' else
> > > "0010" when addr(2 downto 1) = "10" else
> > > "0100" when addr = "110" else
> > > "1000";
> > >
> > > this work.
> > >
> > > why the first version doesn't work?
> > > the symbol '-' means "don't care", isn't it? So why it is wrong?
> > > I prefer something like the first version since is less cryptic.
> > >
> > > thanks
> > I am interested by this issue. Which compiler are you using?
> I use Xilinx Web Pack 5.2.
> both versions compile fine without errors or warning but when I run the
> first model in ModelSim 5.6 I don't obtain what I'm expecting: ce is
> always "1000" except when addr is "110".
>
>
> thanks