-- Copyright © 1993 by McGraw-Hill, Inc. and Zainalabedin Navabi
-- FIGURE 6.3
-- ENTITY DECLERATION OF A FOUR-VALUE INVERTER :
USE WORK.basic_utilities.ALL;
ENTITY inv_q IS
GENERIC (tplh : TIME := 5 NS; tphl : TIME := 3 NS);
PORT (i1 : IN qit; o1 : OUT qit);
END inv_q;
--
-- DOUBLE -DELAY ARCHITECTURE OF INV_Q :
ARCHITECTURE double_delay OF inv_q IS
BEGIN
o1 <= '1' AFTER tplh WHEN i1 = '0' ELSE
'0' AFTER tphl WHEN i1 = '1' OR i1 = 'Z' ELSE
'X' AFTER tplh;
END double_delay;
--