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  #1 (permalink)  
Old 11-13-2007, 05:20 AM
fazulu deen
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Default bidirectional in fpga

Hi ,

Is it possible to implement signal declared as bidirectional
(i.e.,inout) in FPGA.For example i have to declare bidirectional data
bus D[7:0].should i use as two separate unidirectional?

regards,
fazal

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  #2 (permalink)  
Old 11-13-2007, 05:28 AM
mh
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Default Re: bidirectional in fpga

On Nov 13, 10:20 am, fazulu deen <[email protected]> wrote:
> Hi ,
>
> Is it possible to implement signal declared as bidirectional
> (i.e.,inout) in FPGA.For example i have to declare bidirectional data
> bus D[7:0].should i use as two separate unidirectional?
>
> regards,
> fazal



Fazal,
Are you a student or what ?
There must be some one around you to reply to your queries. And keep
one thing in mind: always study some text book before posting a
question.

I cannot understand why some one is willing to make himself a "Butt of
ridicule" in each and every of his post.


/Eldon

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  #3 (permalink)  
Old 11-13-2007, 05:37 AM
Matthew Hicks
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Default Re: bidirectional in fpga

It is possible. In sub-modules, I prefer to use seperate input and output
signals. At the top level, I use the language's bidirectional signal type
and drive it with a value when output is enabled and with z's when the output
isn't. The bidirectional port always drives the input set of signals. Synthesis
tools will implement this however is best for your partcular device.


---Matthew Hicks


> Hi ,
>
> Is it possible to implement signal declared as bidirectional
> (i.e.,inout) in FPGA.For example i have to declare bidirectional data
> bus D[7:0].should i use as two separate unidirectional?
>
> regards,
> fazal



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  #4 (permalink)  
Old 11-13-2007, 06:02 AM
fazulu deen
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Default Re: bidirectional in fpga

On Nov 13, 10:37 am, Matthew Hicks <[email protected]> wrote:
> It is possible. In sub-modules, I prefer to use seperate input and output
> signals. At the top level, I use the language's bidirectional signal type
> and drive it with a value when output is enabled and with z's when the output
> isn't. The bidirectional port always drives the input set of signals. Synthesis
> tools will implement this however is best for your partcular device.
>
> ---Matthew Hicks
>
> > Hi ,

>
> > Is it possible to implement signal declared as bidirectional
> > (i.e.,inout) in FPGA.For example i have to declare bidirectional data
> > bus D[7:0].should i use as two separate unidirectional?

>
> > regards,
> > fazal


Thanks for your suggestions..

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  #5 (permalink)  
Old 11-13-2007, 11:01 AM
Guest
 
Posts: n/a
Default Re: bidirectional in fpga

>Are you a student or what ?
>There must be some one around you to reply to your queries. And keep
>one thing in mind: always study some text book before posting a
>question.
>
>I cannot understand why some one is willing to make himself a "Butt of
>ridicule" in each and every of his post.


Since you seem to be arguing against newsgroups, why are you here?

You say that "There must be some one around you to reply to your
queries". Well, maybe (like me) he works alone. Do you seriously
imagine that the whole world is like the small one that you live in?
Ask some of the sales engineers here. You might be surprised to find
that not everyone who works with FPGAs is a student or works in a
large company, surrounded by willing mentors and a library of relevant
books.

On that subject, which "some text book" do you suggest that he
consult? My own experience is that most of the good-quality material
in this field is provided by manufacturers. These answer many, but
not all of the questions which you seem to feel have an obvious
answer.

As an FPGA novice, I found a similar difficulty with the question
which he asks. The solution is straightforward, but wasn't made
explicit in the manuals which I read. I thought it out for myself,
but I don't think I'd be "a butt of ridicule" if I asked others about
it, especially if I showed that I'd given it some thought. We all
have holes in our knowledge. The contributors here who make me
snigger are not those asking relevant questions. They are those still
working like we did 30 years ago, in the easy environment of a big
company and not having noticed that the rest of the world has moved
on.
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  #6 (permalink)  
Old 11-13-2007, 11:21 AM
commone
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Default Re: bidirectional in fpga

>> > Hi ,
>>
>> > Is it possible to implement signal declared as bidirectional
>> > (i.e.,inout) in FPGA.For example i have to declare bidirectiona

data
>> > bus D[7:0].should i use as two separate unidirectional?

>>
>> > regards,
>> > fazal

>
>Thanks for your suggestions..
>
>


Here I give you an advice. Read the related FPGA datasheets then you wil
know what there are in a FPGA. It is the resources in a FPGA determin
what function a FPGA can implement.

Best regards

Leon,
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  #7 (permalink)  
Old 11-13-2007, 03:46 PM
Andy
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Default Re: bidirectional in fpga

On Nov 13, 5:21 am, "commone" <[email protected]> wrote:
> >> > Hi ,

>
> >> > Is it possible to implement signal declared as bidirectional
> >> > (i.e.,inout) in FPGA.For example i have to declare bidirectional

> data
> >> > bus D[7:0].should i use as two separate unidirectional?

>
> >> > regards,
> >> > fazal

>
> >Thanks for your suggestions..

>
> Here I give you an advice. Read the related FPGA datasheets then you will
> know what there are in a FPGA. It is the resources in a FPGA determine
> what function a FPGA can implement.
>
> Best regards
>
> Leon,


Not exactly...

You can code a bidirectional tri-state bus for most synthesis tools,
and when targeting devices without that capability, they will convert
it to multiplexers.

That said, unidirectional tri-state bus descriptions have some
particular advantages when dealing with mutual exclusiveness of the
select lines. Synthesis assumes that tri-state enables on a bus are
mutually exclusive, whereas coding a non-priority multiplexer with
separate enable bits is sometimes difficult. But bidirectional
internal signals are almost always better when implemented as separate
unidirectional buses, tri-state or not.

Andy

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