C-RAM Group:

Shahid Aslam Khan, Sue Ann Ung and Satneev Bhamra

Application Notes

We have found some things that are very useful while working as a team on the EE 552 project.

• The VHDL quick reference is of a great help when no good textbook reference is available for a quick reference

Last Modified: October 5, 2001

---

VHDL Syntax 

Objective:

This application note provides quick links to common VHDL syntax and provides a list of reserved words.

---

Quick Find: a bc d e f gh i j k lm n o p qr s t u vw x y z keywords attributes

The start symbol is design_file.

---

Syntax:

abstract_literal ::=

decimal_literal | based_literal

access_type_definition ::=

access subtype_indication

actual_designator ::=

expression
| signal_name
| variable_name
| file_name
| open

actual_parameter_part ::=

parameter_association_list

actual_part ::=

actual_designator
| function_name ( actual_designator )
| type_mark ( actual_designator )

adding_operator ::=

+ | - | &

aggregate ::=

( element_association { , element_association } )

alias_declaration ::=

alias alias_designator [ : subtype_indication ] is name [ signature ] ;

alias_designator ::=

identifier
| character_literal
| operator_symbol

allocator ::=

new subtype_indication
| new qualified_expression

architecture_body ::=

architectureidentifier of entity_name is

architecture_declarative_part

begin

architecture_statement_part

end [ architecture ] [ architecture_simple_name ] ;

architecture_declarative_part ::=

{ block_declarative_item }

architecture_statement_part ::=

{ concurrent_statement }

array_type_definition ::=

unconstrained_array_definition | constrained_array_definition

assertion ::=

assert condition

[ report expression ]
[ severity expression ]

assertion_statement ::=

[ label : ] assertion ;

association_element ::=

[ formal_part => ] actual_part

association_list ::=

association_element { , association_element }

attribute_declaration ::=

attribute identifier : type_mark ;

attribute_designator ::=

attribute_simple_name

attribute_name ::=

prefix [ signature ] ' attribute_designator [ ( expression ) ]

attribute_specification ::=

attribute attribute_designator of entity_specification is expression ;

base ::=

integer

base_specifier ::=

B | O | X

base_unit_declaration ::=

identifier ;

based_integer ::=

extended_digit { [underline ] extended_digit }

based_literal ::=

base # based_integer [ . based_integer ] # [ exponent ]

basic_character ::=

basic_graphic_character | format_effector

basic_graphic_character ::=

upper_case_letter | digit | special_character | space_character

basic_identifier ::=

letter { [ underline ] letter_or_digit }

binding_indication ::=

[ use entity_aspect ]
[ generic_map_aspect ]
[ port_map_aspect ]

bit_string_literal ::=

base_specifier " [ bit_value ] "

bit_value ::=

extended_digit { [ underline ] extended_digit }

block_configuration ::=

for block_specification

{ use_clause }
{ configuration_item }

end for ;

block_declarative_item ::=

subprogram_declaration
| subprogram_body
| type_declaration
| subtype_declaration
| constant_declaration
| signal_declaration
| shared_variable_declaration
| file_declaration
| alias_declaration
| component_declaration
| attribute_declaration
| attribute_specification
| configuration_specification
| disconnection_specification
| use_clause
| group_template_declaration
| group_declaration

block_declarative_part ::=

{ block_declarative_item }

block_header ::=

[ generic_clause
[ generic_map_aspect ; ] ]
[ port_clause
[ port_map_aspect ; ] ]

block_specification ::=

architecture_name
| block_statement_label
| generate_statement_label [ ( index_specification ) ]

block_statement ::=

block_label :

block [ ( guard_expression ) ] [ is ]

block_header
block_declarative_part

begin

block_statement_part

end block [ block_label ] ;

block_statement_part ::=

{ concurrent_statement }

case_statement ::=

[ case_label : ]

case expression is

case_statement_alternative
{ case_statement_alternative }

end case [ case_label ] ;

case_statement_alternative ::=

when choices =>

sequence_of_statements

character_literal ::=

' graphic_character '

choice ::=

simple_expression
| discrete_range
| element_simple_name
| others

choices ::=

choice { | choice }

component_configuration ::=

for component_specification

[ binding_indication ; ]
[ block_configuration ]

end for ;

component_declaration ::=

component identifier [ is ]

[ local_generic_clause ]
[ local_port_clause ]

end component [ component_simple_name ] ;

component_instantiation_statement ::=

instantiation_label :

instantiated_unit

[ generic_map_aspect ]
[ port_map_aspect ] ;

component_specification ::=

instantiation_list : component_name

composite_type_definition ::=

array_type_definition
| record_type_definition

concurrent_assertion_statement ::=

[ label : ] [ postponed ] assertion ;

concurrent_procedure_call_statement ::=

[ label : ] [ postponed ] procedure_call ;

concurrent_signal_assignment_statement ::=

[ label : ] [ postponed ] conditional_signal_assignment
| [ label : ] [ postponed ] selected_signal_assignment

concurrent_statement ::=

block_statement
| process_statement
| concurrent_procedure_call_statement
| concurrent_assertion_statement
| concurrent_signal_assignment_statement
| component_instantiation_statement
| generate_statement

condition ::=

boolean_expression

condition_clause ::=

until condition

conditional_signal_assignment ::=

target <= options conditional_waveforms ;

conditional_waveforms ::=

{ waveform when conditionelse }
waveform [ when condition ]

configuration_declaration ::=

configurationidentifier of entity_name is

configuration_declarative_part
block_configuration

end [ configuration ] [ configuration_simple_name ] ;

configuration_declarative_item ::=

use_clause
| attribute_specification
| group_declaration

configuration_declarative_part ::=

{ configuration_declarative_item }

configuration_item ::=

block_configuration
| component_configuration

configuration_specification ::=

for component_specification binding_indication ;

constant_declaration ::=

constant identifier_list : subtype_indication [ := expression ] ;

constrained_array_definition ::=

array index_constraint of element_subtype_indication

constraint ::=

range_constraint
| index_constraint

context_clause ::=

{ context_item }

context_item ::=

library_clause
| use_clause

decimal_literal ::=

integer [ . integer ] [ exponent ]

declaration ::=

type_declaration
| subtype_declaration
| object_declaration
| interface_declaration
| alias_declaration
| attribute_declaration
| component_declaration
| group_template_declaration
| group_declaration
| entity_declaration
| configuration_declaration
| subprogram_declaration
| package_declaration

delay_mechanism ::=

transport
| [ reject time_expression ] inertial

design_file ::=

design_unit { design_unit }

design_unit ::=

context_clause library_unit

designator ::=

identifier | operator_symbol

direction ::=

to | downto

disconnection_specification ::=

disconnectguarded_signal_specification after time_expression ;

discrete_range ::=

discrete_subtype_indication | range

element_association ::=

[ choices => ] expression

element_declaration ::=

identifier_list : element_subtype_definition ;

element_subtype_definition ::=

subtype_indication

entity_aspect ::=

entity entity_name [ ( architecture_identifier ) ]
| configuration configuration_name
| open

entity_class ::=

entity
| architecture
| configuration
| procedure
| function
| package
| type
| subtype
| constant
| signal
| variable
| component
| label
| literal
| units
| group
| file

entity_class_entry ::=

entity_class [ <> ]

entity_class_entry_list ::=

entity_class_entry { , entity_class_entry }

entity_declaration ::=

entity identifier is

entity_header
entity_declarative_part

[ begin

entity_statement_part ]

end [ entity ] [ entity_simple_name ] ;

entity_declarative_item ::=

subprogram_declaration
| subprogram_body
| type_declaration
| subtype_declaration
| constant_declaration
| signal_declaration
| shared_variable_declaration
| file_declaration
| alias_declaration
| attribute_declaration
| attribute_specification
| disconnection_specification
| use_clause
| group_template_declaration
| group_declaration

entity_declarative_part ::=

{ entity_declarative_item }

entity_designator ::=

entity_tag [ signature ]

entity_header ::=

[ formal_generic_clause ]
[ formal_port_clause ]

entity_name_list ::=

entity_designator { , entity_designator }
| others
| all

entity_specification ::=

entity_name_list : entity_class

entity_statement ::=

concurrent_assertion_statement
| passive_concurrent_procedure_call_statement
| passive_process_statement

entity_statement_part ::=

{ entity_statement }

entity_tag ::=

simple_name
| character_literal
| operator_symbol

enumeration_literal ::=

identifier | character_literal

enumeration_type_definition ::=

( enumeration_literal { , enumeration_literal } )

exit_statement ::=

[ label : ] exit [ loop_label ] [ when condition ] ;

exponent ::=

E [ + ] integer | E - integer

expression ::=

relation { and relation }
| relation { or relation }
| relation { xor relation }
| relation [ nand relation ]
| relation [ nor relation ]
| relation { xnor relation }

extended_digit ::=

digit | letter

extended_identifier ::=

\ graphic_character { graphic_character } \

factor ::=

primary [ ** primary ]
| abs primary
| not primary

file_declaration ::=

file identifier_list : subtype_indication [ file_open_information ] ;

file_logical_name ::=

string_expression

file_open_information ::=

[ open file_open_kind_expression ] is file_logical_name

file_type_definition ::=

file of type_mark

floating_type_definition ::=

range_constraint

formal_designator ::=

generic_name
| port_name
| parameter_name

formal_parameter_list ::=

parameter_interface_list

formal_part ::=

formal_designator
| function_name ( formal_designator )
| type_mark ( formal_designator )

full_type_declaration ::=

type identifier is type_definition ;

function_call ::=

function_name [ ( actual_parameter_part ) ]

generate_statement ::=

generate_label :

generation_scheme generate

[ {block_declarative_item }

begin ]

{ concurrent_statement }

end generate [ generate_label ] ;

generation_scheme ::=

for generate_parameter_specification
| if condition

generic_clause ::=

generic ( generic_list ) ;

generic_list ::=

generic_interface_list

generic_map_aspect ::=

generic map ( generic_association_list )

graphic_character ::=

basic_graphic_character | lower_case_letter | other_special_character

group_constituent ::=

name | character_literal

group_constituent_list ::=

group_constituent { , group_constituent }

group_declaration ::=

group identifier : group_template_name ( group_constituent_list ) ;

group_template_declaration ::=

group identifier is ( entity_class_entry_list ) ;

guarded_signal_specification ::=

guarded_signal_list : type_mark

identifier ::=

basic_identifier | extended_identifier

identifier_list ::=

identifier { , identifier }

if_statement ::=

[ if_label : ]

if condition then

sequence_of_statements

{ elsif condition then

sequence_of_statements }

[ else

sequence_of_statements ]

end if [ if_label ] ;

incomplete_type_declaration ::=

type identifier ;

index_constraint ::=

( discrete_range { , discrete_range } )

index_specification ::=

discrete_range
| static_expression

index_subtype_definition ::=

type_mark range <>

indexed_name ::=

prefix ( expression { , expression } )

instantiated_unit ::=

[ component ] component_name
| entity entity_name [ ( architecture_identifier ) ]
| configuration configuration_name

instantiation_list ::=

instantiation_label { , instantiation_label }
| others
| all

integer ::=

digit { [ underline ] digit }

integer_type_definition ::=

range_constraint

interface_constant_declaration ::=

[ constant ] identifier_list : [ in ] subtype_indication [ := static_expression ]

interface_declaration ::=

interface_constant_declaration
| interface_signal_declaration
| interface_variable_declaration
| interface_file_declaration

interface_element ::=

interface_declaration

interface_file_declaration ::=

file identifier_list : subtype_indication

interface_list ::=

interface_element { ; interface_element }

interface_signal_declaration ::=

[ signal ] identifier_list : [ mode ] subtype_indication [ bus ] [ := static_expression ]

interface_variable_declaration ::=

[ variable ] identifier_list : [ mode ] subtype_indication [ := static_expression ]

iteration_scheme ::=

while condition
| for loop_parameter_specification

label ::=

identifier

letter ::=

upper_case_letter | lower_case_letter

letter_or_digit ::=

letter | digit

library_clause ::=

library logical_name_list ;

library_unit ::=

primary_unit
| secondary_unit

literal ::=

numeric_literal
| enumeration_literal
| string_literal
| bit_string_literal
| null

logical_name ::=

identifier

logical_name_list ::=

logical_name { , logical_name }

logical_operator ::=

and | or | nand | nor | xor | xnor

loop_statement ::=

[ loop_label : ]

[ iteration_scheme ] loop

sequence_of_statements

end loop [ loop_label ] ;

miscellaneous_operator ::=

** | abs | not

mode ::=

in | out | inout | buffer | linkage

multiplying_operator ::=

* | / | mod | rem

name ::=

simple_name
| operator_symbol
| selected_name
| indexed_name
| slice_name
| attribute_name

next_statement ::=

[ label : ] next [ loop_label ] [ when condition ] ;

null_statement ::=

[ label : ] null ;

numeric_literal ::=

abstract_literal
| physical_literal

object_declaration ::=

constant_declaration
| signal_declaration
| variable_declaration
| file_declaration

operator_symbol ::=

string_literal

options ::=

[ guarded ] [ delay_mechanism ]

package_body ::=

package bodypackage_simple_name is

package_body_declarative_part

end [ package body ] [ package_simple_name ] ;

package_body_declarative_item ::=

subprogram_declaration
| subprogram_body
| type_declaration
| subtype_declaration
| constant_declaration
| shared_variable_declaration
| file_declaration
| alias_declaration
| use_clause
| group_template_declaration
| group_declaration

package_body_declarative_part ::=

{ package_body_declarative_item }

package_declaration ::=

package identifier is

package_declarative_part

end [ package ] [ package_simple_name ] ;

package_declarative_item ::=

subprogram_declaration
| type_declaration
| subtype_declaration
| constant_declaration
| signal_declaration
| shared_variable_declaration
| file_declaration
| alias_declaration
| component_declaration
| attribute_declaration
| attribute_specification
| disconnection_specification
| use_clause
| group_template_declaration
| group_declaration

package_declarative_part ::=

{ package_declarative_item }

parameter_specification ::=

identifier in discrete_range

physical_literal ::=

[ abstract_literal ] unit_name

physical_type_definition ::=

range_constraint

units

primary_unit_declaration
{ secondary_unit_declaration }

end units [ physical_type_simple_name ]

port_clause ::=

port ( port_list ) ;

port_list ::=

port_interface_list

port_map_aspect ::=

port map ( port_association_list )

prefix ::=

name
| function_call

primary ::=

name
| literal
| aggregate
| function_call
| qualified_expression
| type_conversion
| allocator
| ( expression )

primary_unit ::=

entity_declaration
| configuration_declaration
| package_declaration

procedure_call ::=

procedure_name [ ( actual_parameter_part ) ]

procedure_call_statement ::=

[ label : ] procedure_call ;

process_declarative_item ::=

subprogram_declaration
| subprogram_body
| type_declaration
| subtype_declaration
| constant_declaration
| variable_declaration
| file_declaration
| alias_declaration
| attribute_declaration
| attribute_specification
| use_clause
| group_template_declaration
| group_declaration

process_declarative_part ::=

{ process_declarative_item }

process_statement ::=

[ process_label : ]

[ postponed ] process [ ( sensitivity_list ) ] [ is ]

process_declarative_part

begin

process_statement_part

end [ postponed ] process [ process_label ] ;

process_statement_part ::=

{ sequential_statement }

qualified_expression ::=

type_mark ' ( expression )
| type_mark ' aggregate

range ::=

range_attribute_name
| simple_expression directionsimple_expression

range_constraint ::=

range range

record_type_definition ::=

record

element_declaration
{ element_declaration }

end record [ record_type_simple_name ]

relation ::=

shift_expression [ relational_operatorshift_expression ]

relational_operator ::=

= | /= | < | <= | > | >=

report_statement ::=

[ label : ]

report expression

[ severityexpression ] ;

return_statement ::=

[ label : ] return [ expression ] ;

scalar_type_definition ::=

enumeration_type_definition
| integer_type_definition
| floating_type_definition
| physical_type_definition

secondary_unit ::=

architecture_body
| package_body

secondary_unit_declaration ::=

identifier = physical_literal ;

selected_name ::=

prefix . suffix

selected_signal_assignment ::=

with expression select

target <= options selected_waveforms ;

selected_waveforms ::=

{ waveform when choices , }
waveform when choices

sensitivity_clause ::=

on sensitivity_list

sensitivity_list ::=

signal_name { , signal_name }

sequence_of_statements ::=

{ sequential_statement }

sequential_statement ::=

wait_statement
| assertion_statement
| report_statement
| signal_assignment_statement
| variable_assignment_statement
| procedure_call_statement
| if_statement
| case_statement
| loop_statement
| next_statement
| exit_statement
| return_statement
| null_statement

shift_expression ::=

simple_expression [ shift_operatorsimple_expression ]

shift_operator ::=

sll | srl | sla | sra | rol | ror

sign ::=

+ | -

signal_assignment_statement ::=

[ label : ] target <= [ delay_mechanism ] waveform ;

signal_declaration ::=

signal identifier_list : subtype_indication [ signal_kind ] [ := expression ] ;

signal_kind ::=

register | bus

signal_list ::=

signal_name { , signal_name }
| others
| all

signature ::=

[ [ type_mark { , type_mark } ] [ return type_mark ] ]

simple_expression ::=

[ sign ] term { adding_operator term }

simple_name ::=

identifier

slice_name ::=

prefix ( discrete_range )

string_literal ::=

" { graphic_character } "

subprogram_body ::=

subprogram_specification is

subprogram_declarative_part

begin

subprogram_statement_part

end [ subprogram_kind ] [ designator ] ;

subprogram_declaration ::=

subprogram_specification ;

subprogram_declarative_item ::=

subprogram_declaration
| subprogram_body
| type_declaration
| subtype_declaration
| constant_declaration
| variable_declaration
| file_declaration
| alias_declaration
| attribute_declaration
| attribute_specification
| use_clause
| group_template_declaration
| group_declaration

subprogram_declarative_part ::=

{ subprogram_declarative_item }

subprogram_kind ::=

procedure | function

subprogram_specification ::=

procedure designator [ ( formal_parameter_list ) ]
| [ pure | impure ] function designator [ ( formal_parameter_list ) ]

return type_mark

subprogram_statement_part ::=

{ sequential_statement }

subtype_declaration ::=

subtype identifier is subtype_indication ;

subtype_indication ::=

[ resolution_function_name ] type_mark [ constraint ]

suffix ::=

simple_name
| character_literal
| operator_symbol
| all

target ::=

name
| aggregate

term ::=

factor { multiplying_operatorfactor }

timeout_clause ::=

for time_expression

type_conversion ::=

type_mark ( expression )

type_declaration ::=

full_type_declaration
| incomplete_type_declaration

type_definition ::=

scalar_type_definition
| composite_type_definition
| access_type_definition
| file_type_definition

type_mark ::=

type_name
| subtype_name

unconstrained_array_definition ::=

array ( index_subtype_definition { , index_subtype_definition } )

of element_subtype_indication

use_clause ::=

use selected_name { , selected_name } ;

variable_assignment_statement ::=

[ label : ] target := expression ;

variable_declaration ::=

[ shared ] variable identifier_list : subtype_indication [ := expression ] ;

wait_statement ::=

[ label : ] wait [ sensitivity_clause ] [ condition_clause ] [ timeout_clause ] ;

waveform ::=

waveform_element { , waveform_element }
unaffected

waveform_element ::=

value_expression [ after time_expression ]
| null [ after time_expression ]

---

Reserved Words

A: abs, access, after, alias, all, and, architecture, array, assert, attribute,

B: begin, block, body, buffer, bus,
C: case, component, configuration, constant,
D: disconnect, downto,
E: else, elsif, end, entity, exit,
F: file, for, function,
G: generate, generic, group, guarded,
I: if, impure, in, inertial, inout, is,
L: label, library, linkage, literal, loop,
M: map, mod,
N: nand, new, next, nor, not, null,
O: of, on, open, or, others, out,
P: package, port, postponed, procedure, process, pure,
R: range, record, register, reject, rem, report, return, rol, ror,
S: select, severity, shared, signal, sla, sll, sra, srl, subtype,
T: then, to, transport, type,
U: unaffected, units, until, use,
V: variable,
W: wait, when, while, with,
X: xnor, xor

---

Predefined Attributes

(T = scalar type or subtype, A = array type, S = signal, E = named entity)

T'BASE
T'LEFT
T'RIGHT
T'HIGH
T'LOW
T'ASCENDING
T'IMAGE(X)
T'VALUE(X)
T'POS(X)
T'VAL(X)
T'SUCC(X)
T'PRED(X)
T'LEFTOF(X)
T'RIGHTOF(X)

A'LEFT[(N)]
A'RIGHT[(N)]
A'HIGH[(N)]
A'LOW[(N)]
A'RANGE[(N)]
A'REVERSE_RANGE[(N)]
A'LENGTH[(N)]
A'ASCENDING[(N)]

S'DELAYED[(T)]
S'STABLE[(T)]
S'QUIET[(T)]
S'TRANSACTION
S'EVENT
S'ACTIVE
S'LAST_EVENT
S'LAST_ACTIVE
S'LAST_VALUE
S'DRIVING
S'DRIVING_VALUE

E'SIMPLE_NAME
E'INSTANCE_NAME
E'PATH_NAME

---

Reference: VHDL 1993 Syntax reprinted from IEEE Std 1076-1993 "IEEE Standard VHDL Language Reference Manual," Copyright © 1993 by the Institute of Electrical and Electronics Engineers, Inc.

---