l6_operators and attributes

8/6/2019 L6_Operators and Attributes

1/26

5/7/2011 DSD,USIT,GGSIPU 1

Operators Assignment Operators

Logical Operators Relational Operators

Shift Operators

Adding Operators Multiplying Operators

Miscellaneous Operators


2/26


Assignment Operators Used to assign values to signals, variables

and constants.

Used to assign values to individual

vector elements or with OTHERS.


3/26


Logical Operators The seven Logical Operators

AND

OR

NAND are not associative

NOR are not associative

XOR XNOR

NOT ; highest precedence over the others


4/26


Relational Operator = Equality

/= inequality

=

Must be one-dimensional discrete array of the

same type.


5/26


Shift Operators Sll Shift left logical

Srl Shift right logical

Sla Shift left arithmetic

Sra Shift right arithmetic

Rol Rotate left Ror Rotate Right


6/26


A = 10101100

B


7/26


Adding Operators + addition

- subtraction

& Concatenation

Example:

A = 1010

B = 1000

C


8/26


Multiplying Operators * Multiplication

/ Division

Mod modulus

Rem Remainder


9/26


Miscellaneous Operators Abs Absolute

** Exponentiation

Not negation


10/26


Attributes An attributes is a value, function, type,

range, signal or a constant that may be

associated with one or more names within a

VHDL description.

Two types of attributes

User defined attributes Predefined attributes


11/26


Classes of attributes1. Value attributes : Return a constant value

2. Function attributes : Call a function that return a value

3. Signal Attributes : Creates a new implicit signal

4. Type Attributes : Return a type

5. Range attributes : Returns a range

To use a attribute the (apostrophe) construct must

be employed


12/26


Type Attributes TBase Returns the base type of datatype it is

attached to

example:Naturalbase returns integer

TLeft Returns left value specified in typedeclaration

Example:

IntegerLeft is 2147483647

Bitleft is 0


13/26


Tright Returns right value specified in

type declaration

Example:

Integerright is 2147483647

bitright is 1 Thigh Returns largest value specified in

declaration

Example:

Type bit8 is 255 downto 0

bit8high is 255


14/26


Tlow Returns smallest value specified in

declarationExample:

Type bit8 is 255 downto 0;

bit8low is 0;

Tpos(x) Returns position number of

argument in type (first position is 0)

Example:

Type color is (red,green, blue, orange);

colorpos(green) is 1;


15/26


Tval(x) Returns value in type at specified

position numberExample:


colorval(3) is orange;

Tsucc(x) Returns the successor to the

value passed in

Example:

Type color is (red,green, blue, orange);colorsucc(green) is blue;


16/26


Tpred(x) Returns the predecessor to

the value passed inExample:


colorpred(blue) is green;

Tleftof(x) Returns the value to the left

of the value passed in

Example:

Type color is (red,green, blue, orange);colorleftof(blue) is green


17/26


Trightof(x) Returns the value to the right

of the value passed inExample:

Type color is (red,green,blue,orange);

colorrightof(blue) is orange;

Type s is (1,0,0,1,0,1)

Srightof(1)


18/26


Signal attributes Sevent

Function returning a boolean that identifies if

signal S has a new value assigned onto thissignal (I.e. value is different that last value)

Returns TRUE when an event occurs on s.

If clkevent then . if clk just changed in

value than Wait until clkevent and clk=1 ;-- rising edge

of clock


19/26


Signal attribute (cont..) Sstable

Implicit signal of Boolean type. This implicit

signal has the value TRUE when an event

(change in value) has not occurred on signal S

for T time units and the value FALSE

otherwise. If time is omitted, it defaults to 0ns.

Returns TRUE if no event has occurred on s

If sstable(40ns) then met set up time


20/26


Sactive Sactive

Function returning a boolean that identifies ifsignal S had a new assignment made onto it(whether the value of the assignment is theSAME or DIFFERENT).

Returns TRUE if s = 1

If sactive then. New assignment of S

Wait on sactive;

Wait until sactive;


21/26


Signal attribute (cont..) Squiet

This implicit signal has the value TRUE when the

signal has been quiet (I.e. no activity or signalassignment) for T time units, and the value FALSE

otherwise. If time is omitted, it defaults to 0ns.

Returns TRUE if no event has occurred during the time

specified

If squiet(40ns) then Really quiet, not even an

assignment of the same value during the last T time

units.


22/26


Signal attributes (cont..) SLast_event

Function returning the amount of time that has elapsed

since the last event (change in value) occurred on signalS. If there was no previous event, it returns Timehigh

(The maximum value for time)

Returns the time elapsed since last event

Variable : TsinceLastEvent:time; .

TsinceLastEvent :slast_event;


23/26


SLast_active

Returns the time elapsed since last s=1


24/26


Signal attribute (cont.) Slast_value

Returns the value of s before the last event

Stransaction

Signal of type bit that changes for every

transaction on s

Sdelayed Signal same as s delayed by specified time


25/26


User-defined Attributes Syntax

Attribute Declaration:

ATTRIBUTE attribute_name: attribute_type; Attribute specification:

ATTRIBUTE attribute_name of target_name : class isvalue;

Where:Attribute_type : any data type (bit,std_logic etc)

Class : type, signal,function etc.

Value : 0, 27, 000101110 , etc


26/26


Generic Generic is a way of specifying a generic

parameter

A static parameter that can be easily modifiedand adapted to different applications.

A generic statement, when employed must bedeclared in the entity.

Syntax:Generic (parameter_name : parameter_type:=

parameter_value);

l6_operators and attributes

Documents