楼 主:skeyy 2003年5月11日09:11

 麻烦高手帮我解决一个vhdl问题 ！
在 std_logic_1164 里面定义的一些语句如下，请高手帮忙解释一下
CONSTANT resolution_table:stdlogic_table:=(
('U','U','U','U','U','U','U','U','U'),--U
('U','X','X','X','X','X','X','X','X'),--X
('U','X','0','X','0','0','0','0','X'),--0
('U','X','X','1','1','1','1','1','X'),--1
('U','X','0','1','Z','W','L','H','X'),--Z
('U','X','0','1','W','W','W','W','X'),--W
('U','X','0','1','L','W','L','W','X'),--L
('U','X','0','1','H','W','W','H','X'),--H
('U','X','X','X','X','X','X','X','X'),-- -
);

FUNCTION resolved(s:std_ulogic_vector) RETURN std_ulogic IS
VARIABLE result:std_ulogic:='Z';
BEGIN
IF (s'LENGTH=1) THEN RETURN s(s'LOW);
ELSE
FOR i IN s'RANGE LOOP
result:=resolution_table(result,s(i));
END LOOP;
END IF;
RETURN result;
END resolved;

CONSTANT and_table:stdlogic_table:=(
('U','U','0','U','U','U','0','U','U'),--U
('U','X','0','X','X','X','0','X','X'),--X
('0','0','0','0','0','0','0','0','X'),--0
('U','X','0','1','x','x','0','1','X'),--1
('U','X','0','X','X','X','0','X','X'),--Z
('U','X','0','X','X','X','0','X','X'),--W
('O','0','0','0','0','0','0','0','0'),--L
('U','X','0','1','X','X','0','1','X'),--H
('U','X','0','X','X','X','0','X','X'),-- -
);

麻烦高手给讲解一下这两个表格分别是什么意思，不胜感激！