module comp4 
title '4-bit look-ahead comparator 
Charles Olivier & Mary Bailey    Data I/O Corp.   24 Feb 1984'

	IC1	device 'P16HD8';

	A3,A2,A1,A0	pin	1,2,3,4;
	B3,B2,B1,B0	pin	5,6,7,8;
	E3,E2,E1,E0	pin	14,15,16,17;
	A_NE_B,A_EQ_B	pin	12,13;
	A_GT_B,A_LT_B	pin	18,19;

	No,Yes	= 0,1;
	A	= [A3,A2,A1,A0];
	B	= [B3,B2,B1,B0];
	E	= [E3,E2,E1,E0];
	C0	macro {(A0>B0)};
	C1	macro {(A1>B1) # E1 & (C0)};
	C2	macro {(A2>B2) # E2 & (C1)};

equations
	E	= A !$ B;	"intermediate An = Bn

	A_EQ_B	= E3 & E2 & E1 & E0;

	A_NE_B	= !A_EQ_B;

	A_GT_B	= (A3>B3) # E3 & (C2);

	A_LT_B	= !A_GT_B & !A_EQ_B;

test_vectors  'test for A = B'
       ([ A, B] -> [A_EQ_B, A_GT_B, A_LT_B, A_NE_B])
	[ 0, 0] -> [ Yes  ,   No  ,   No  ,   No  ];
	[ 1, 1] -> [ Yes  ,   No  ,   No  ,   No  ];
	[ 2, 2] -> [ Yes  ,   No  ,   No  ,   No  ];
	[ 5, 5] -> [ Yes  ,   No  ,   No  ,   No  ];
	[ 8, 8] -> [ Yes  ,   No  ,   No  ,   No  ];
	[10,10] -> [ Yes  ,   No  ,   No  ,   No  ];
	[15,15] -> [ Yes  ,   No  ,   No  ,   No  ];

test_vectors  'test for A > B'
       ([ A, B] -> [A_EQ_B, A_GT_B, A_LT_B, A_NE_B])
	[ 1, 0] -> [  No  ,  Yes  ,   No  ,  Yes  ];
	[ 2, 1] -> [  No  ,  Yes  ,   No  ,  Yes  ];
	[ 4, 3] -> [  No  ,  Yes  ,   No  ,  Yes  ];
	[ 8, 7] -> [  No  ,  Yes  ,   No  ,  Yes  ];
	[15,14] -> [  No  ,  Yes  ,   No  ,  Yes  ];
	[ 6, 2] -> [  No  ,  Yes  ,   No  ,  Yes  ];
	[ 5, 0] -> [  No  ,  Yes  ,   No  ,  Yes  ];

test_vectors  'test for A < B'
       ([ A, B] -> [A_EQ_B, A_GT_B, A_LT_B, A_NE_B])
	[ 3, 9] -> [  No  ,   No  ,  Yes  ,  Yes  ];
	[14,15] -> [  No  ,   No  ,  Yes  ,  Yes  ];
	[ 7, 8] -> [  No  ,   No  ,  Yes  ,  Yes  ];
	[ 3, 4] -> [  No  ,   No  ,  Yes  ,  Yes  ];
	[ 2, 8] -> [  No  ,   No  ,  Yes  ,  Yes  ];
end comp4