Assigning values to a multidimential array

[Johnsy Joseph]

Hello Everybody,

I would be grateful if somebody helped me with this. I have the
following definitions.

type byte is array(7 downto 0) of std_logic;
type sarray is array(6 downto 1) of byte;

variable shift_register:sarray;
variable shftreg_data: std_logic_vector(7 downto 0);


I would like to do the something like this-

shift_register(0)(7 to 0) := shftreg_data(7 to 0);

I basically want to assign a vector to one of the elements of my array
of vectors but it isnt working. I am using VHDL'87 but it doesnt
compile. Any methods to do such a thing?

Thanks for the help
Warm Regards
Johnsy

 

[Nicolas Matringe]

Johnsy Joseph a écrit:

Hello Everybody,

I would be grateful if somebody helped me with this. I have the
following definitions.

type byte is array(7 downto 0) of std_logic;
type sarray is array(6 downto 1) of byte;

variable shift_register:sarray;
variable shftreg_data: std_logic_vector(7 downto 0);


I would like to do the something like this-

shift_register(0)(7 to 0) := shftreg_data(7 to 0);

I basically want to assign a vector to one of the elements of my array
of vectors but it isnt working. I am using VHDL'87 but it doesnt
compile. Any methods to do such a thing?

Hi
VHDL is a strongly typed language. You can not assign a value to a
signal/variable if their types don't match.
In your example, shftreg_data is std_logic_vector and shift_register(0)
is byte so you can't do it.
Luckily, their types are closely related: they are made of elements of
the same type. You can juste type cast your value:
shift_register(0)(7 to 0) := byte(shftreg_data(7 to 0));

 

[Egbert Molenkamp]

Some remarks:
1. You defined a new type byte. This is not the same type as
std_logic_vector and therefore the assignment
shift_register(0)(7 to 0) := shftreg_data(7 to 0); has problems with
incompatible types.
Suggestion: use a subtype for byte:
SUBTYPE byte IS std_logic_vector(7 downto 0);

2. shift_register(0)(7 to 0) notice that element 0 is not in the range om 6
downto 1 (see type declaration of sarray).

3. you mix up "downto" and "to". If your vector is declared as a "downto"
then a slice of that vector should also be a "downto".

So a corrected piece of code looks like:

subtype byte is std_logic_vector( 7 downto 0);
type sarray is array(6 downto 0) of byte;

variable shift_register:sarray;
variable shftreg_data: std_logic_vector(7 downto 0);

shift_register(0)(7 downto 0) := shftreg_data(7 downto 0);

Egbert Molenkamp

 

[Johnsy Joseph]

Thank you very much Friends !!!
It works.

Warm Regards
Johnsy

 

[Jim Lewis]

Going one step further from what Egbert wrote,
you can leave off the lower level of indicies:

shift_register(0) := shftreg_data;

Also if your are going to define the subtype byte,
then you ought to use it when you declare shftreg_data:
variable shftreg_data: byte;

Or alternately, don't use byte at all:
type sarray is array(6 downto 0) of std_logic_vector(7 downto 0);

Cheers,
Jim
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