An external resistor and capacitor set a time constant. One-shots produce output pulses, the width set by the time constant, in response to certain changes in their inputs. "Well duh". Try a manufacturer's website, i.e. National Semiconductor's Application Note #366, "Designer's Encyclopedia of One Shots", at http://www.national.com/an/AN/AN-366.pdf or Fairchild Semiconductor for the 74123 data sheet http://www.fairchildsemi.com/pf/DM/DM74123.html If you have a nearby university, you'll be able to find the 74123 in just about any TTL databook from the last 25 years or so. While you're there, you might find a copy of Horowitz and Hill's _The Art of Electronics_. Note that the 74LS123 is incompatible, for many applications, with the non-LS 74123. This is the boundary between analog and digital technology... -- Tim Shoppa Email: shoppa(a)trailing-edge.com Trailing Edge Technology WWW: http://www.trailing-edge.com/ 7328 Bradley Blvd Voice: 301-767-5917 Bethesda, MD, USA 20817 Fax: 301-767-5927