On Mon, May 2, 2016 at 3:19 PM, Brent Hilpert <[email protected]> wrote:
> On 2016-May-02, at 2:39 PM, Charles Anthony wrote: > > On Mon, May 2, 2016 at 1:21 PM, Paul Koning <[email protected]> > wrote: > >>> On May 2, 2016, at 3:59 PM, Mattis Lind <[email protected]> wrote: > >>> > >>> Yet another nice color brochure. > >>> > >>> https://dl.dropboxusercontent.com/u/96935524/Datormusuem/lab11.pdf > >>> > >>> Has anyone seen a VR20 in real? Rather interesting to be able to do a > red > >>> and green X/Y screen based on different energy levels. Someone care to > >>> explain how that works? > >> > >> See https://en.wikipedia.org/wiki/Penetron. The idea is that there are > >> two layers, and a high voltage beam pokes through the first to activate > the > >> second. > >> > > I'm not sure that the Penetron is what DEC was using; according to > > http://homepage.cs.uiowa.edu/~jones/pdp8/man/vc8e.html: > > > > "If the CO (color) bit changes because of the value loaded, and if the > VC8E > > is equipped to handle this option, a timer will be started to set the DN > > (done) bit after either 300 microseconds (green to red) or 1600 > > microseconds (red to green). These delays correspond to the time taken by > > the VR20 display for these color changes." > > > > According the Penetron wiki page, additional activation energy was > provided > > by a "set of fine wires placed behind the screen"; whereas the VC8E > > apparently is setting the color by timing the beam. > > > > So yes, it seems to be an activation energy phenomenon, but not > > specifically the Penetron technology. My physics fu isn't good enough to > > explain how, but I would guess at some very non-linear phosphorescence > > response. > > > > Might have had to do with the time taken to switch the HV supply (for a > Penetron) for the different penetration levels rather than a different > phosphor-exciting scheme. Although, is that interface even at the scan > level relating directly to the display tube, or at a controller level where > it might be an artifact of the controller electronics? Context: I have never seen any of these beasts, and I am a s/w guy that dabbles in h/w. All of my opinions herein are derived from my reading DEC documents to write vector display emulators. I may talking through my hat here.... http://bitsavers.informatik.uni-stuttgart.de/www.computer.museum.uq.edu.au/pdf/DEC-11-HLPMA-B-D%20LPS11-S%20Laboratory%20Peripheral%20System%20Maintenance%20Manual.pdf "3.4.6.2 Green Mode -- ... The intensify pule is used to intensify the point on the scope. ... approximately 1 us." "3.4.6.2 Red Mode -- ... 6 us." I can't locate any VR20 documentation, so other than pulse width input to the VR20 I am unable to speculate further; it may well be that Penetron technology was used, but the wording of the controller made it seem to me otherwise, but I am more than prepared to be wrong -- it is perfectly possible that the VR20 is controlling a Penetron based on the pulse width. -- Charles
