Data Types - Computer Science - Lecture Slides, Slides of Computer Science

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Data Types

• Each data object has a type associated with

it.

• The type defines the set of values that the

object can have and the set of operation that

are allowed on it.

Data types defined in the

standard package

• Predefined data type are as follows:
  • Bit
  • Bit_vector
  • Boolean
  • Character
  • File_open_kind*
  • File_open_status*
  • Integer
  • Natural
  • Positive
  • Real
  • Severity_level
  • String
  • Time* Docsity.com

Data Types

• A type declaration defines the name of the

type and the range of the type.

• Type declaration are allowed in package

declaration sections, entity declaration

sections, architecture declaration sections,

subprogram declaration section and process

declaration sections.

Scalar Types

• Scalar types describe objects that can hold ,

at most, one value at a time.

• Integer Type
  • It is same as mathematical integers.
  • All of the normal predefined mathematical function apply to integer types.
  • Minimum Range: -2,147,483,647 to 12,147,483,

Example - Integer

Architecture test of test is

Begin

Process (x) Variable a: integer; Begin a := 1; --ok a := -1 ; -- ok a := 1.0; -- error End process;

End test;

Example – Real Types

Architecture test of test is

signal a : real;

Begin

a <= 1.0; -- ok a <= 1; -- error a <= -1.0E10; -- ok a <= 1.5E-20; --ok a <= 5.3 ns; -- error

End test;

Enumerated types

• Enumerated type is used to represent exactly the values required for a specific operation.
• All of the values of an enumerated type are user- defined.
• This values can be identifiers or single-character literals.
• A typical example:

TYPE fourval IS (‘x’, ‘0’, ‘1’, ‘z’); TYPE color IS (red,yellow, blue,green,orange);

Physical Types

• Physical types are used to represent physical quantities such as distance,current, time and so on.
• A physical type provides for a base unit,and successive units are then defined in terms of this unit.
• The smallest unit represented is one base unit.
• The largest unit is determined by the range specified in physical type declaration.
• TIME is a predefined physical types

Example – Physical Type

Package example is

type current is range 0 to 10000000000 units na; ua = 1000 na; -- nano amp ma = 1000 ua; -- micro amp a = 1000 ma; End units; type load_factor is (small, med, big);

End example;

Predefined physical type - Time

Type TIME is Range

units fs; --femtosecond ps = 1000 fs; -- picosecond ns = 1000 ps; -- nansecond us = 1000 ns; -- microsecond ms = 1000 us; -- millisecond sec = 1000 ms; -- second min = 60 sec; -- minute hr = 60 min; -- hour

End units;

Composite Types

• Arrays Type are groups of elements of the

same type.

• Arrays are useful for modeling linear structure such as RAMs and ROMs.
• Record Types allow the grouping of

elements of different types.

• Record are useful for modeling data packets, instructions and so on.

Array slices and Ranges

• Assignment of arrays preserves the left-to-

right ordering regardless of the direction.

• Example

Signal x : std_logic_vector(0 to 3);--case 1 Signal y : std_logic_vector(3 downto 0); --case X <= “1010”; Y <= “0101”;

Cont..

• The assignment x<=y is equivalent to:

X(0) <= Y(3); -- the left element X(1) <= y(2); X(2) <=Y(1); X(3) <=Y(0); -- the right elements The array range for case I in 0 to 3 loop, the elements of the array would be accessed from left to right. The array range for caseII in 3 downto 0 loop, the elements of the array would be accessed from right to left.