Types defined in std_logic_1164 Package

• Type STD_LOGIC

  • 9 logic value system (‘U’, ‘X’, ‘0’, ‘1’, ‘Z’, ‘W’, ‘L’, ‘H’, ‘-’)
    • ‘W’, ‘L’, ‘H” weak values (Not supported by Synthesis)
    • ‘X’ - used for unknown
    • ‘Z’ - (not ‘z’) used for tri-state
    • ‘-’ Don’t Care
  • Resolved type: supports, signals with multiple drives.
    

• Type STD_ULOGIC

  • Same 9 value system as STD_LOGIC
  • Unresolved type: Does not support multiple signal drives. Error will occur.

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