Previous

std_logic_misc Package

The std_logic_misc package has been added to the IEEE package and does not have to be compiled into a separate VHDL library.

This package resides in the Xilinx Foundation synthesis libraries directory ($XILINX/synth/lib/packages/IEEE/src/std_logic_misc.vhd). The std_logic_misc package declares the primary data types supported by the Synopsys VSS Family.

Boolean reduction functions use one argument, an array of bits, and return a single bit. For example, the and-reduction of “101” is “0”, the logical AND of all three bits.

Several functions in the std_logic_misc package provide Boolean reduction operations for the predefined type STD_LOGIC_VECTOR. The following example shows the declarations of these functions.

   function AND_REDUCE  (ARG: STD_LOGIC_VECTOR) return UX01;
   function NAND_REDUCE (ARG: STD_LOGIC_VECTOR) return UX01;
   function OR_REDUCE   (ARG: STD_LOGIC_VECTOR) return UX01;
   function NOR_REDUCE  (ARG: STD_LOGIC_VECTOR) return UX01;
   function XOR_REDUCE  (ARG: STD_LOGIC_VECTOR) return UX01;
   function XNOR_REDUCE (ARG: STD_LOGIC_VECTOR) return UX01;
   function AND_REDUCE  (ARG: STD_ULOGIC_VECTOR) return UX01;
   function NAND_REDUCE (ARG: STD_ULOGIC_VECTOR) return UX01;
   function OR_REDUCE   (ARG: STD_ULOGIC_VECTOR) return UX01;
   function NOR_REDUCE  (ARG: STD_ULOGIC_VECTOR) return UX01;
   function XOR_REDUCE  (ARG: STD_ULOGIC_VECTOR) return UX01;
   function XNOR_REDUCE (ARG: STD_ULOGIC_VECTOR) return UX01;

These functions combine the bits of STD_LOGIC_VECTOR, as the name of the function indicates. For example, XOR_REDUCE returns the XOR value of all bits in ARG.

The example below shows some reduction function calls and their return values.

   AND_REDUCE("111") = '1'
   AND_REDUCE("011") = '0'
   
   OR_REDUCE("000")  = '0'
   OR_REDUCE("001")  = '1'
   
   XOR_REDUCE("100") = '1'
   XOR_REDUCE("101") = '0'
   
   NAND_REDUCE("111") = '0'
   NAND_REDUCE("011") = '1'
   
   NOR_REDUCE("000") = '1'
   NOR_REDUCE("001") = '0'
   
   XNOR_REDUCE("100") = '0'
   XNOR_REDUCE("101") = '1'
Next