Selectric Typewriter conversions

on 4/2/03 3:36 AM, Eric Smith at eric(a)brouhaha.com wrote: For what it's worth, my memory (no less fuzzy than Eric's) remembers that as a model 735. But even with the more robust "I/O Selectrics" there was a hidden gotcha: when you sent data to the mechanism you had to time it right. The Selectric needed varying amounts of time to tilt and swivel the type element, depending on the letter chosen. To cope with that, lots of the early computer interface projects just stuck a software delay loop in the driver code to wait plenty of time for each letter to finish printing before it sent the next character code to the Selectric. This apparently caused a lot of mechanical wear-and-tear as the clutch relentlessly cycled in and out, and even the heavy duty "I/O" mechanism would eventually crap out from all the lurching. The right way to do it was to make sure your driver polled the state of some microswitches that IBM had thoughtfully buried in the clockwork to provide feedback on the progress of the print cycle. That way you could start sending a new character at a magic moment just _before_ the previous print cycle fully finished, which provided the fastest possible printing and extended the life of the clutch. Like John said, VooDoo. Regards, Arlen Michaels