basic question about data types

Hi,

I have some basic question about data types in vhdl. I hope you can give
me an answer. Which library should I use in new designs (numeric_std or
std_logic_unsigned)? The unsigned type is a vector type?

Thank your for your answer.

bye

martin sauer

Martin Sauer

Hi,

I have an example:

In my VHDL code I have two unsigned signals

signal sDataR : unsigned (9 downto 0);
signal sR : unsigned (1 downto 0);

I want to add bit 1 of sR to sDataR. sDataR + sR(1) doesn't work. I will
get the following error:

ERROR: cannot convert type std_ulogic to type unsigned

How can I add one bit of an unsigned signal to another unsigned signal?

Thank you for your answer.

bye

martin sauer

Martin Sauer schrieb:
> Hi,
>
> I have some basic question about data types in vhdl. I hope you can give
> me an answer. Which library should I use in new designs (numeric_std or
> std_logic_unsigned)? The unsigned type is a vector type?
>
> Thank your for your answer.
>
> bye
>
> martin sauer

Martin Sauer

On 1 Dec, 08:00, Martin Sauer <m...@displaign.de> wrote:
> Hi,
>
> I have an example:
>
> In my VHDL code I have two unsigned signals
>
> signal sDataR : unsigned (9 downto 0);
> signal sR : unsigned (1 downto 0);
>
> I want to add bit 1 of sR to sDataR. sDataR + sR(1) doesn't work. I will
> get the following error:
>
> ERROR: cannot convert type std_ulogic to type unsigned
>
> How can I add one bit of an unsigned signal to another unsigned signal?
>
> Thank you for your answer.
>
> bye
>
> martin sauer
>
> Martin Sauer schrieb:
>
> > Hi,
>
> > I have some basic question about data types in vhdl. I hope you can give
> > me an answer. Which library should I use in new designs (numeric_std or
> > std_logic_unsigned)? The unsigned type is a vector type?
>
> > Thank your for your answer.
>
> > bye
>
> > martin sauer
>
>

Definatly use numeric_std, because it is an actual IEEE standard,
std_logic_unsigned is not - it was origionally defined by Synopsys and
compiled (wrongly) in to the IEEE library. Different vendors implement
std_logic_unsigned differently, whereas the IEEE defined numeric_std.

As for your error, sR(1) is just a single bit, which is why you're
getting the problem. Addition has to be done on 2 unsigned numbers
that have the same length that match the result length. So, the best
way around your problem:

signal output : unsigned(10 downto 0); --addition output will be 1
bit bigger than largest input if you dont want overflow
...
output <= ('0' & sDataR) + resize(sR, output'length);
--'0' is concatenated the make sDataR 11 bits.

if you really wanted to add a single bit from sR then you have to use
a range to keep it as an unsigned type. Indexing just 1 returns a
std_ulogic, as you found.:

output <= ('0' & sDataR) + resize(sR(1 downto 1), output'length);

Tricky

Martin Sauer wrote:
> Hi,
>
> I have an example:
>
> In my VHDL code I have two unsigned signals
>
> signal sDataR : unsigned (9 downto 0);
> signal sR : unsigned (1 downto 0);
>
> I want to add bit 1 of sR to sDataR. sDataR + sR(1) doesn't work. I will
> get the following error:
>
> ERROR: cannot convert type std_ulogic to type unsigned
>
> How can I add one bit of an unsigned signal to another unsigned signal?
>
> Thank you for your answer.
>
> bye
>
> martin sauer
>
> Martin Sauer schrieb:
> > Hi,
> >
> > I have some basic question about data types in vhdl. I hope you can give
> > me an answer. Which library should I use in new designs (numeric_std or
> > std_logic_unsigned)? The unsigned type is a vector type?
> >

operator '+' is defined in std_logic_unsigned for logic vectors. So
you can do it like

use ieee.std_logic_unsigned;
.....
srout <= sDataR + sR(1 downto 1);

It will certainly compile

Regards

olekk

> operator '+' is defined in std_logic_unsigned for logic vectors. So
> you can do it like
>


See above 2 posts

Tricky

Hi all,

thank you for your fast answer.

Now it works fine.

bye

martin sauer

olekk schrieb:
>
> Martin Sauer wrote:
>> Hi,
>>
>> I have an example:
>>
>> In my VHDL code I have two unsigned signals
>>
>> signal sDataR : unsigned (9 downto 0);
>> signal sR : unsigned (1 downto 0);
>>
>> I want to add bit 1 of sR to sDataR. sDataR + sR(1) doesn't work. I will
>> get the following error:
>>
>> ERROR: cannot convert type std_ulogic to type unsigned
>>
>> How can I add one bit of an unsigned signal to another unsigned signal?
>>
>> Thank you for your answer.
>>
>> bye
>>
>> martin sauer
>>
>> Martin Sauer schrieb:
>>> Hi,
>>>
>>> I have some basic question about data types in vhdl. I hope you can give
>>> me an answer. Which library should I use in new designs (numeric_std or
>>> std_logic_unsigned)? The unsigned type is a vector type?
>>>
>
> operator '+' is defined in std_logic_unsigned for logic vectors. So
> you can do it like
>
> use ieee.std_logic_unsigned;
> ....
> srout <= sDataR + sR(1 downto 1);
>
> It will certainly compile
>
> Regards

Martin Sauer

Martin Sauer a écrit :
> Hi all,
>
> thank you for your fast answer.
>
> Now it works fine.

The quick and ugly way. Read the other answers please. Please. I
*really* mean it.

Nicolas

Nicolas Matringe