Thursday, 27 November 2014

VHDL IEEE PACKAGES - DATA TYPES – DATA CONVERSIONS

VHDL IEEE PACKAGES - DATA TYPES – DATA CONVERSIONS
IEEE PACKAGE:
The IEEE library contains several packages, including the following:
  • std_logic_1164: Specifies the STD_LOGIC (8 levels) and STD_ULOGIC (9 levels) multi-valued logic systems.
  • std_logic_arith: Specifies the SIGNED and UNSIGNED data types and related arithmetic and comparison operations. It also contains several data conversion functions, which allow one type to be converted into another: conv_integer(p), conv_unsigned(p, b), conv_signed(p, b), conv_std_logic_vector(p, b).
  • std_logic_signed: Contains functions that allow operations with STD_LOGIC_VECTOR data to be performed as if the data were of type SIGNED.
  • std_logic_unsigned: Contains functions that allow operations with STD_LOGIC_VECTOR data to be performed as if the data were of type UNSIGNED.
  • std_logic_textio: Contains functions text i/o, file read & write, etc.

Pre-Defined Data Types
VHDL contains a series of pre-defined data types, specified through the IEEE 1076 and IEEE 1164 standards. More specifically, such data type definitions can be found in the following packages / libraries:
  • Package standard of library std: Defines BIT, BOOLEAN, INTEGER, and REAL data types.
  • Package std_logic_1164 of library ieee: Defines STD_LOGIC and STD_ULOGIC data types.
  • Package std_logic_arith of library ieee: Defines SIGNED and UNSIGNED data types, plus several data conversion functions, like conv_integer(p), conv_unsigned(p, b), conv_signed(p, b), and conv_std_logic_vector(p, b).
  • Packages std_logic_signed and std_logic_unsigned of library ieee: Contain functions that allow operations with STD_LOGIC_VECTOR data to be performed as if the data were of type SIGNED or UNSIGNED, respectively.




DATA CONVERSIONS:
Several data conversion functions can be found in the std_logic_arith package of
the ieee library. They are:
  • conv_integer(p) : Converts a parameter p of type INTEGER, UNSIGNED, SIGNED, or STD_ULOGIC to an INTEGER value. Notice that STD_LOGIC_VECTOR is not included.
  • conv_unsigned(p, b): Converts a parameter p of type INTEGER, UNSIGNED, SIGNED, or STD_ULOGIC to an UNSIGNED value with size b bits.
  • conv_signed(p, b): Converts a parameter p of type INTEGER, UNSIGNED, SIGNED, or STD_ULOGIC to a SIGNED value with size b bits.
  • conv_std_logic_vector(p, b): Converts a parameter p of type INTEGER, UNSIGNED, SIGNED, or STD_LOGIC to a STD_LOGIC_VECTOR value with size b bits.


The following are the examples for converting interger to std logic vector, unsigned, singed and std logic vector to integer, and integer to real & complex, and integer to string. By converting std logic vector to integer, and that integer value to string, we can convert std logic vector to string.
INTEGER TO SLV/UNSIGNED/SIGNED
num is integer
USE IEEE.NUMERIC_STD.ALL;
dat <=std_logic_vector(to_unsigned(55,dat'length));

use ieee.std_logic_arith.all;--NEVER USE STD LOGIC ARITH & NUMERIC_STD TOGETHER
slv<= conv_std_logic_vector(num,slv’length);
unsignd := conv_unsigned(num,unsignd’length);
signd := conv_signed(num,signd’length);

SLV TO INTEGER
USE IEEE.STD_LOGIC_UNSIGNED.ALL;
variable inte:natural;
--dat= std_logic_vector 11 downto 0
inte:=conv_integer(dat); -- to integer
INTEGER TO STRING
report "dat= " & integer'image(inte); --to string

INTEGER TO REAL/COMPLEX
num is integer
USE IEEE.MATH_REAL.ALL;
real_num := real(inte);
complx := complex(inte);

Coming soon: Basic VHDL Syntaxes & Constructs, Detailed and latest file read write with hexadecimal, octal, binary data types….. Stay tuned.


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