US patent number 4,689,604  (those of us who are dyslexic hate trying to
                             read 7 digit patent numbers the way they are
                             usually given with no spaces or commas)

For full details:
        http://patent.womplex.ibm.com/details?patent_number=4689604

See also US patent number 5,302,965 titled "Display"
        http://patent.womplex.ibm.com/details?patent_number=5302965

My friends Jim Philips and Richard Ottosen invented the same thing in
1980 or 1981, but weren't smart enough to file a patent application.  As
others have pointed out, though, it really just seems like an application
of well-known techniques.

Eric