Compact Summary of VHDL phần 4 doc

frlg = 660 ft; -- furlong

mi = 5280 ft; -- mile

lg = 3 mi; -- league

end units;

access type declaration

Declare a type for creating access objects, pointers.

An object of an access type must be of class variable.

An object

type identifier is access subtype_indication;

type node_ptr is access node;

variable root : node_ptr := new node'("xyz", 0, null, null, red);

variable item : node := root.all;

file type declaration

Declare a type for creating file handles.

type identifier is file of type_mark ;

type my_text is file of string ;

type word_file is file of word ;

file output : my_text;

file_open(output, "my.txt", write_mode);

write(output, "some text"&lf);

file_close(output);

file test_data : word_file;

file_open(test_data, "test1.dat", read_mode);

read(test_data, word_value);

subtype declaration

Declare a type that is a subtype of an existing type.

Note that type creates a new type while subtype

creates a type that is a constraint of an existing type.

subtype identifier is subtype_indication ;

subtype name_type is string(1 to 20) ;

variable a_name : name_type := "Doe, John ";

VHDL Declaration Statements

http://www.csee.umbc.edu/help/VHDL/declare.html (3 of 9) [22/12/2001 15:23:39]