🚀 go-pugleaf

Hi all,

    Another person here at Intel saw a problem with the proposed 9-value 
    logic package; I thought I'd post it, and maybe start a discussion.

    Below is an extract from the v2.800 package posted to the net. The
    concern is with the don't care state. It used to be '-', now it 
    is 'D'.

--     v2.300   |  wdb   |  10/24/90  | Changed '-' to 'D', deleted attributes
--     v2.400   |  wdb   |  11/12/90  | Fixed subtyped subtypes
--     v2.500   |  wdb   |  01/02/91  | Change output types of overloaded operators
--     v2.600   |  wdb   |  01/04/91  | Clean UP
--     v2.700   |  wdb   |  01/08/91  | Add Conversion functions to Bit
--     v2.800   |  wdb   |  03/03/91  | Pre-Ballot Cleanup
-- --------------------------------------------------------------------
-- Library IEEE; -- proposed location of this package
-- --------------------------------------------------------------------

PACKAGE logic_system is

    -------------------------------------------------------------------    
    -- Logic State System  (unresolved)
    -------------------------------------------------------------------    
    TYPE std_ulogic is ( 'U',  -- Unitialized
                         'X',  -- Forcing  0 or 1
                         '0',  -- Forcing  0
                         '1',  -- Forcing  1
                         'Z',  -- High Impedance   
                         'W',  -- Weak     0 or 1
                         'L',  -- Weak     0     ( for ECL open emitter )
                         'H',  -- Weak     1     ( for open Drain or Collector )
                         'D'   -- don't care
                       );
 
      If you had a vector of this type (say, an address) wouldn't the don't 
      care type get confused with the hex value D? This especially comes 
      into play when you have a simulator who's waveform display can show 
      user-defined types (like this one) as hex. 

      What was wrong with '-' as don't care, anyway?


Richard Newton II			         rnewton@mrmngo.intel.com
Intel Corp., 2625 Walsh Ave, Mail Stop SC4-69, Santa Clara, CA 95052-8122