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Literals

Used In

  • Expression

Reference Manual

VHDL-93:
  • Section 7.3.1
  • Section 13.4
  • Section 3.1.1
  • Section 3.1.3

Syntax

See reference manual.

Rules and Examples

Numeric literals with a decimal point are real, those without are integer:

constant FREEZE : integer := 32;
constant TEMP : real := 32.0;

Numeric literals may be expressed in any base from 2 to 16. They may also be broken up using underscore, for clarity.

A_INT <= 16#FF#;
B_INT <= 2#1010_1010#;
MONEY := 1_000_000.0;

Real numbers may be expressed in exponential form:

FACTOR := 2.2E-6;

Literals of type time (and other physical types) must have units. The units should be preceded by a space, although some tools may not require this:

constant DEL1 : time := 10 ns;
constant DEL2 : time := 2.27 us;

Literals of enumerated types may either be characters (as for bit and std_logic), or identifiers:

type MY_LOGIC is ('X','0','1','Z');
type T_STATE is (IDLE, READ, END_CYC);
signal CLK : MY_LOGIC := '0';
signal STATE : T_STATE := IDLE;

Synthesis Issues

Logic synthesis tools may not support named association fully. Also, record assignments using aggregates may not be supported.