18 Mar
2005
18 Mar
'05
10:01 p.m.
Peter C. Wallace wrote:
Okay, now my age and lack of experience is going to show: Can someone explain
to me exactly *how* a light pen works? What is the feedback mechanism if
drawing on, say, a completely black screen? How does the computer get
coordinates for where the pen is touching?
--
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Want to help an ambitious games project? http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
Long
persistence phospor doesn't preclude the use of a light pen, it
just introduces some limitations on the usage model. The DEC Type 30
and 340 displays as used on the PDP-1 through PDP-10 use a P7 phosphor
which has very high persistence, yet light pens were commonly used with
them.
You can cheat with P7 and other double layer phosphors by using a blue
filter as they have a medium or short persistance blue phosphor and a
very long persistance yellow or orange phosphor.