United States Patent [19] [ii] Patent Number: 4,764,764
Mulkern [45] Date of Patent: Aug. 16, 1988
[54] WRITE-PROTECT APPARATUS FOR BIT MAPPED MEMORY
[75] Inventor: Joseph Mulkern, St. Paul, Minn.
[73] Assignee: Honeywell Inc., Minneapolis, Minn.
[21] Appl. No.: 675,112
[22] Filed: Nov. 27, 1984
[51] Int. Q." G09G 1/00
[52] U.S. a 340/724; 340/721;
340/747
[58] Field of Search 340/721, 723, 724, 747,
340/750, 798, 799
[56] References Cited
U.S. PATENT DOCUMENTS
3,497,760 2/1970 Kiesling 340/722
3,639,736 2/1972 Sutherland 340/724
3,889,107 6/1975 Sutherland 340/747
3,996,673 12/1976 Vorst et al 340/747
4,492,956 1/1985 Collmeyer et al 340/723
4,663,618 5/1987 Hayles et al 340/732
Primary Examiner—Marshall M. Curtis
Assistant Examiner—Mahmoud Fakahigar
Attorney, Agent, or Firm—Seymour Levine; Albin
Medved
[57] ABSTRACT
A pattern write protect system approximates a memory area for data entry with a multiplicity of rectangles and determines when a point for entry is within the window by establishing a relative position of the address point coordinates to the coordinates of the sides of the rectangles. A less than/greater than signal for each address coordinate relative to the sides of each rectangle is derived. These signals are summed and the resulting sum signals are then multiplied to provide an enable gate signal.
6 Claims, 3 Drawing Sheets
