------------Original Message: Date: Thu, 1 Feb 2007 22:11:24 -0500 From: "Ethan Dicks" <ethan.dicks at gmail.com> <snip> Long ago, I did hang a pair of Radio Shack 7-segment LEDs off of a PET User Port with some trivial logic to use the 8th bit to select digit A vs digit B, then the lower 7 bits of the port went right to the segments. A small machine-language routine tapped into the 60Hz clock interrupt refreshed the digits. For a modern machine, I'd recommend some sort of external latch and multiplexer at least, or perhaps a dedicated LED driver like the ICL7218 (MAX7218?) (here's one I made a while back with 16 digits from one parallel port and two driver chips) http://www.penguincentral.com/retrocomputing/retrogaming/scoreboard.html -ethan ------------Comment: For driving 7seg displays or LEDs, I'd recommend an MC14489; it'll directly drive 5 mux'ed 7 segment displays (hex or pseudo-alpha), straight binary, or 25 LEDs from a 3 wire DC to 3MHz serial interface. Saves a lot of wiring, especially if you use multi-digit displays; just the thing for a blinkenlights panel... mike