Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!linus!wivax!decvax!harpo!seismo!hao!hplabs!sri-unix!kevinw%isl@BRL.ARPA From: kevinw%isl@BRL.ARPA Newsgroups: net.micro Subject: Re: brain damaged (?) keyboards (Commodore 64/VIC 20) Message-ID: <2543@sri-arpa.UUCP> Date: Fri, 24-Jun-83 20:42:00 EDT Article-I.D.: sri-arpa.2543 Posted: Fri Jun 24 20:42:00 1983 Date-Received: Mon, 27-Jun-83 03:49:22 EDT Lines: 16 Since the keyboard is scanned by software driven by the IRQ line (for the 20, I'm sure the 64 also) one can insert a wedge (sombody's bright idea of a name for a kludge between the outside world and the inner machine) at the IRQ address and scan the keyboard directly. I think that there also may be a place to actually insert a new keyboard scanner -- there is one for the display driver. The keyboard is scanned by the A and B ports on a 6522/6526 and the algorithm (at least on the 20) is super simple and has variable (+ and -) key rollover (sometimes you get char's for free, and sometimes it isn't the char you typed...). As long as they are using a diode crosspoint keyswitch matrix it is possible to encode true N key rollover... Thus the keyboard can be made to look like a full ASCII keyboard if you don't mind the wrong (or modified) keytops. Happy munging! -- Kevin